<PAGE>   1
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM 10-K


(Mark One)

[X]      ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
         EXCHANGE ACT OF 1934 (FEE REQUIRED)

                   FOR THE FISCAL YEAR ENDED DECEMBER 31, 1999

                                       OR

[ ]      TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
         EXCHANGE ACT OF 1934 (NO FEE REQUIRED)

             For the transition period from __________ to __________

                          COMMISSION FILE NO. 33-13437

                          DEL TACO INCOME PROPERTIES IV
                       (A California limited partnership)
               (Exact name of registrant specified in its charter)

                   CALIFORNIA                                  33-0241855
  (State or other jurisdiction of incorporation or          (I.R.S. Employer
                  organization)                           Identification Number)

          23041 AVENIDA DE LA CARLOTA
            LAGUNA HILLS, CALIFORNIA                               92653
    (Address of principal executive offices)                     (Zip Code)

       Registrant's telephone number, including area code: (949) 462-9300

        Securities registered pursuant to section 12(b) of the Act: None

        Securities registered pursuant to section 12(g) of the Act: None

        Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ]

                       DOCUMENTS INCORPORATED BY REFERENCE

        Portions of the registrant's Form S-11 Registration Statement filed June
5, 1987 are incorporated by reference into Part IV of this report.



<PAGE>   2

                                     PART I

ITEM 1. BUSINESS

The partnership is a publicly-held limited partnership organized under the
California Uniform Limited Partnership Act. The partnership's General Partner is
Del Taco, Inc., a California corporation ("General Partner"). The partnership
sold 165,415 units totaling $4.135 million through an offering of limited
partnership units from June 1987 through June 1988. The term of the partnership
agreement is until December 31, 2027 unless terminated earlier by means provided
in the partnership agreement.

The business of the partnership is ownership and leasing of restaurants in
California to Del Taco, Inc. The partnership acquired land and constructed three
Mexican-American restaurants for long-term lease to Del Taco, Inc. Each property
is leased for 32 years on a triple net basis. Rent is equal to twelve percent of
gross sales of the restaurants. As of December 31, 1999, the partnership had a
total of three properties leased to Del Taco (Del Taco, in turn, has sub-leased
one of the restaurants to a Del Taco franchisee).

The partnership has no full time employees. The partnership agreement assigns
full authority for general management and supervision of the business affairs of
the partnership to the General Partner. The General Partner has a one percent
interest in the profits or losses and distributions of the partnership. Limited
partners have no right to participate in the management or conduct of the
partnership's business affairs.




                                        2

<PAGE>   3

ITEM 2. PROPERTIES

The partnership has acquired three properties with proceeds obtained from the
sale of limited partnership units:


<TABLE>
<CAPTION>
                                                                                                   Date of
                                                 Date of                Restaurant               Commencement
Address                 City, State            Acquisition             Constructed             of Operation(1)
-------                 -----------            -----------             -----------             ----------------
<S>                    <C>                     <C>                    <C>                     <C>
Orangethorpe            Placentia,             August 5, 1988          60 seat with drive      March 27, 1989
Avenue                  CA                                             through service
                                                                       window
Lakeshore               Lake Elsinore,         February 1, 1989        60 seat with drive      April 18, 1990(2)
Drive                   CA                                             through service
                                                                       window
Highland Avenue         San Bernardino,        December 8, 1989        60 seat with drive      July 13, 1990
                        CA                                             through service
                                                                       window
</TABLE>

(1)     Commencement of operation is the first date Del Taco, Inc., as lessee,
        operated the facility on the site as a Del Taco restaurant.

(2)     The restaurant is subleased to a franchisee of Del Taco, Inc. and the
        restaurant operates as a Del Taco restaurant.


                                     PART II


ITEM 3. LEGAL PROCEEDINGS

The partnership is not a party to any material pending legal proceedings.


ITEM 4. SUBMISSIONS OF MATTERS TO A VOTE OF SECURITY HOLDERS

None.

ITEM 5. MARKET FOR THE PARTNERSHIP'S COMMON EQUITY AND RELATED SECURITY HOLDER
MATTERS

The partnership sold 165,415 ($4,135,375) limited partnership units during the
public offering period ended June 3, 1988 and currently has 339 limited partners
of record. There is no public market for the trading of the units. Distributions
made by the partnership to the limited partners during the past three fiscal
years are described in Note 7 to the Notes to the Financial Statements contained
under Item 8.




                                       3
<PAGE>   4

ITEM 6. SELECTED FINANCIAL DATA

<TABLE>
<CAPTION>
                                                   FOR THE YEAR ENDED DECEMBER 31,
                             1999              1998              1997             1996               1995
                          ----------        ----------        ----------        ----------        ----------
<S>                       <C>               <C>               <C>               <C>               <C>
Rental revenue            $  401,101        $  398,071        $  327,956        $  361,980        $  275,561

Interest and
  other income                 3,223             2,455             2,326             1,244             1,193

Net income                   258,596           254,610           187,583           219,223           134,697

Net income
  per limited
  partnership
  unit(1)                       1.55              1.52              1.12              1.31              0.81

Cash distributions
  per limited
  partnership
  unit                          2.16              1.83              1.70              1.74              1.45

Total assets               2,198,920         2,298,687         2,334,746         2,429,366         2,495,331

Long-term
  obligations                137,953           137,953           137,953           137,953           137,953
</TABLE>



(1)     The net income per limited partnership unit was calculated based upon
        165,375 weighted average units outstanding in 1999 and 165,415 weighted
        average units outstanding in 1998, 1997, 1996 and 1995.


                                       4
<PAGE>   5

ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS

Liquidity and Capital Resources

The partnership offered limited partnership units for sale between June 1987 and
June 1988. 14.5% of the $4.135 million raised through sale of limited
partnership units was used to pay commissions to brokers and to reimburse the
General Partner for offering costs incurred. Approximately $3 million of the
remaining funds were used to acquire sites and build three restaurants. In
February of 1992, approximately $442,000 raised during the offering but not
required to acquire sites and build restaurants was distributed to the limited
partners.

The three restaurants leased to Del Taco make up almost all of the income
producing assets of the partnership. Therefore, the business of the partnership
is almost entirely dependent on the success of the Del Taco trade name
restaurants that lease the properties. The success of the restaurants is
dependent on a large variety of factors, including, but not limited to, consumer
demand and preference for fast food, in general, and for Mexican-American food
in particular.

Results of Operations

The partnership owns three properties that are under long-term lease to Del Taco
for restaurant operations (Del Taco, in turn, has sub-leased one of the
restaurants to a Del Taco franchisee).



                                       5
<PAGE>   6

ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS - (Continued)

Results of Operations - Continued

The following table sets forth rental revenue earned by restaurant for the year:


<TABLE>
<CAPTION>
                                                           YEAR ENDED DECEMBER 31,
                                                1999                1998                1997
                                              --------            --------            --------
<S>                                           <C>                 <C>                 <C>
Orangethorpe Ave., Placentia, CA              $174,429            $172,184            $142,585

Lakeshore Drive, Lake Elsinore, CA             142,724             144,180             119,218

Highland Ave., San Bernardino, CA               83,948              81,707              66,153
                                              --------            --------            --------
          Total                               $401,101            $398,071            $327,956
                                              ========            ========            ========
</TABLE>


The partnership receives rental revenues equal to 12 percent of gross sales from
the restaurants. The partnership earned rental revenue of $401,101 during the
year ended December 31, 1999, which represents an increase of $3,030 from 1998.
The increase in rental revenue was caused primarily by an increase in
supplemental rent at the restaurants under lease.

The following table breaks down general and administrative expenses by type of
expense:


                                    PERCENTAGE OF TOTAL GENERAL & ADMIN. EXPENSE


<TABLE>
<CAPTION>
                                                          Year Ended December 31,
                                               1999               1998               1997
                                              ------             ------             ------
<S>                                            <C>                <C>                <C>
Accounting fees                                65.78%             64.94%             64.37%
Distribution of
   information to limited partners             32.32              33.16              33.58
Other                                           1.90               1.90               2.05
                                              ------             ------             ------
                                              100.00%            100.00%            100.00%
                                              ======             ======             ======
</TABLE>

Certain reclassifications have been made to the 1998 and 1997 amounts in the
table above to conform to the current year presentation.

General and administrative costs increased from 1998 to 1999 due to increased
costs for accounting and income tax return preparation.

Net income increased by $3,986 from 1998 to 1999 due to the increase in revenues
of $3,798 and decrease in depreciation expense of $367, which was partially
offset by the $179 increase in general and administrative expenses.

On May 19, 1998, the special limited partner resigned. Consistent with the
partnership agreement, the General Partner assumed the duties and
responsibilities of the special limited partner.



                                       6
<PAGE>   7


ITEM 8. FINANCIAL STATEMENTS


PART I.  INFORMATION


<TABLE>
<CAPTION>
                                                                                            PAGE NUMBER
                                                                                            -----------
<S>                                                                                         <C>
                                            INDEX

Report of Independent Public Accountants                                                          8

Balance Sheets at December 31, 1999 and 1998                                                      9

Statements of Income for the years ended
  December 31, 1999, 1998 and 1997                                                               10

Statement of Changes in Partners' Equity for
  the three years ended December 31, 1999                                                        11

Statements of Cash Flows for the years ended
  December 31, 1999, 1998 and 1997                                                               12

Notes to Financial Statements                                                                 13-17
</TABLE>






                                       7
<PAGE>   8
                          [ARTHUR ANDERSEN LETTERHEAD]




REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS


To the Partners of
Del Taco Income Properties, IV:

We have audited the accompanying balance sheets of Del Taco Income Properties IV
(a California Limited Partnership) as of December 31, 1999 and 1998, and the
related statements of income, partners' equity and cash flows for the years then
ended. These financial statements and the schedule referred to below are the
responsibility of the Partnership's management. Our responsibility is to express
an opinion on these financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free from
material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements. An audit
also includes assessing the accounting principles used and significant estimates
made by management, as well as evaluating the overall financial statement
presentation. We believe that our audits provide a reasonable basis for our
opinion.

In our opinion, the financial statements referred to above present fairly, in
all material respects, the financial position of Del Taco Income Properties IV
as of December 31, 1999 and 1998, and the results of its operations and its cash
flows for the years then ended in conformity with generally accepted accounting
principles.

Our audits were made for the purpose of forming an opinion on the basic
financial statements taken as a whole. The schedule in the index of the
financial statements is presented for purposes of complying with the Securities
and Exchange Commission's rules and is not part of the basic financial
statements. This schedule has been subjected to the auditing procedures applied
in our audits of the basic financial statements and, in our opinion, fairly
states in all material respects, the financial data required to be set forth
therein in relation to the basic financial statements taken as a whole.



/s/ ARTHUR ANDERSEN LLP
------------------------------
 Arthur Andersen LLP



Orange County, California
March 1, 2000











                                       8

<PAGE>   9

                          DEL TACO INCOME PROPERTIES IV

                                 BALANCE SHEETS



<TABLE>
<CAPTION>
                                                           DECEMBER 31,
                                                  1999                     1998
                                               -----------             -----------
<S>                                            <C>                     <C>
                                      ASSETS

CURRENT ASSETS:
     Cash                                      $   100,224             $   101,404
     Receivable from Del Taco, Inc.                111,622                 106,724
     Deposits                                          400                     504
                                               -----------             -----------
        Total current assets                       212,246                 208,632
                                               -----------             -----------
PROPERTY AND EQUIPMENT, AT COST:
     Land and improvements                       1,236,700               1,236,700
     Buildings and improvements                  1,289,860               1,289,860
     Machinery and equipment                       484,789                 484,789
                                               -----------             -----------
                                                 3,011,349               3,011,349
     Less--accumulated depreciation              1,024,675                 921,294
                                               -----------             -----------
                                                 1,986,674               2,090,055
                                               -----------             -----------

                                               $ 2,198,920             $ 2,298,687
                                               ===========             ===========

                         LIABILITIES AND PARTNERS' EQUITY

CURRENT LIABILITIES:
     Payable to limited partners               $    19,309             $    18,684
     Accounts payable                                7,362                   5,271
                                               -----------             -----------
        Total current liabilities                   26,671                  23,955
                                               -----------             -----------

OBLIGATION TO GENERAL PARTNER                      137,953                 137,953
                                               -----------             -----------

PARTNERS' EQUITY:
     Limited partners                            2,045,087               2,146,545
     General Partner-Del Taco, Inc.                (10,791)                 (9,766)
                                               -----------             -----------
                                                 2,034,296               2,136,779
                                               -----------             -----------
                                               $ 2,198,920             $ 2,298,687
                                               ===========             ===========
</TABLE>



   The accompanying notes are an integral part of these financial statements.



                                       9
<PAGE>   10

                          DEL TACO INCOME PROPERTIES IV

                              STATEMENTS OF INCOME



<TABLE>
<CAPTION>
                                                        YEAR ENDED DECEMBER 31,
                                             1999                1998               1997
                                           --------            --------            --------
<S>                                        <C>                 <C>                 <C>
REVENUES:
     Rent                                  $401,101            $398,071            $327,956
     Interest                                 2,698               1,555               1,651
     Other                                      525                 900                 675
                                           --------            --------            --------
                                            404,324             400,526             330,282
                                           --------            --------            --------
EXPENSES:
     General and administrative              42,347              42,168              38,951
     Depreciation                           103,381             103,748             103,748
                                           --------            --------            --------
                                            145,728             145,916             142,699
                                           --------            --------            --------
        Net income                         $258,596            $254,610            $187,583
                                           ========            ========            ========
     Net income per limited
        partnership unit                   $   1.55            $   1.52            $   1.12
                                           ========            ========            ========
</TABLE>




   The accompanying notes are an integral part of these financial statements.



                                       10
<PAGE>   11

                         DEL TACO INCOME PROPERTIES IV

                    STATEMENT OF CHANGES IN PARTNERS' EQUITY

                      THREE YEARS ENDED DECEMBER 31, 1999



<TABLE>
<CAPTION>
                                               Limited Partners
                                      -----------------------------------              General
                                          Units                  Amount                 Partner                  Total
                                      -----------             -----------             -----------             -----------
<S>                                  <C>                     <C>                     <C>                     <C>
Balance, December 31, 1996                165,415             $ 2,293,656             $    (8,281)            $ 2,285,375
   Net income                                  --                 185,707                   1,876                 187,583
   Cash distributions                          --                (281,950)                 (2,848)               (284,798)
                                      -----------             -----------             -----------             -----------

Balance, December 31, 1997                165,415               2,197,413                  (9,253)              2,188,160
   Net income                                  --                 252,064                   2,546                 254,610
   Cash distributions                          --                (302,932)                 (3,059)               (305,991)
                                      -----------             -----------             -----------             -----------

Balance, December 31, 1998                165,415               2,146,545                  (9,766)              2,136,779
   Redemption of units                        (40)                     --                      --                      --
   Net income                                  --                 256,010                   2,586                 258,596
   Cash distributions                          --                (357,468)                 (3,611)               (361,079)
                                      -----------             -----------             -----------             -----------
Balance, December 31, 1999                165,375             $ 2,045,087             $   (10,791)            $ 2,034,296
                                      ===========             ===========             ===========             ===========
</TABLE>



   The accompanying notes are an integral part of these financial statements.




                                       11
<PAGE>   12

                          DEL TACO INCOME PROPERTIES IV

                            STATEMENTS OF CASH FLOWS



<TABLE>
<CAPTION>
                                                                                   YEAR ENDED DECEMBER 31,
                                                                      1999                 1998                   1997
                                                                   ---------             ---------             ---------
<S>                                                                <C>                   <C>                   <C>
CASH FLOWS FROM OPERATING ACTIVITIES:

Net income                                                         $ 258,596             $ 254,610             $ 187,583
Adjustments to reconcile net income to net
  cash provided by operating activities:
     Depreciation                                                    103,381               103,748               103,748
     Increase (decrease) in payable to limited partners                  625                16,181                  (535)
     Increase in receivable from General Partner                      (4,898)              (41,592)              (13,574)
     (Decrease) increase in accounts payable                           2,091                  (859)                3,130
     Decrease (increase) in deposits                                     104                  (104)                    -
                                                                   ---------             ---------             ---------
           Net cash provided by operating activities                 359,899               331,984               280,352

CASH FLOWS FROM FINANCING ACTIVITIES:
Cash distributions to partners                                      (361,079)             (305,991)             (284,798)
                                                                   ---------             ---------             ---------

NET (DECREASE) INCREASE IN CASH                                       (1,180)               25,993                (4,446)

BEGINNING CASH BALANCE                                               101,404                75,411                79,857
                                                                   ---------             ---------             ---------

ENDING CASH BALANCE                                                $ 100,224             $ 101,404             $  75,411
                                                                   =========             =========             =========
</TABLE>



   The accompanying notes are an integral part of these financial statements.



                                       12
<PAGE>   13


                          DEL TACO INCOME PROPERTIES IV

                          NOTES TO FINANCIAL STATEMENTS

                                DECEMBER 31, 1999



NOTE 1 - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

THE PARTNERSHIP: Del Taco Income Properties IV (a California limited
partnership) was formed on March 23, 1987, for the purpose of acquiring real
property in California for construction of three Mexican-American restaurants to
be leased under long-term agreements to Del Taco, Inc. (General Partner for
operation under the Del Taco trade name).

BASIS OF ACCOUNTING: The partnership utilizes the accrual method of accounting
for transactions relating to the business of the partnership. Distributions are
made to the General and limited partners in accordance with the provisions of
the partnership agreement (see Note 2).

PROPERTY AND EQUIPMENT: Property and equipment is stated at cost. Depreciation
is computed using the straight-line method over estimated useful lives which are
20 years for land improvements, 35 years for buildings and improvements, and 10
years for machinery and equipment.

The partnership accounts for property and equipment in accordance with Statement
of Financial Accounting Standards (SFAS) No. 121, "Accounting for the Impairment
of Long Lived Assets and for Long Lived Assets to be Disposed of." SFAS 121
requires that long-lived assets be reviewed for impairment whenever events or
changes in circumstances indicate that the carrying value of the asset may not
be recoverable. In evaluating long-lived assets held for use, an impairment loss
is recognized if the sum of the expected future cash flows (undiscounted and
without interest charges) is less than the carrying value of the asset. Once a
determination has been made that an impairment loss should be recognized for
long-lived assets, various assumptions and estimates are used to determine fair
value including, among others, estimated costs of construction and development,
recent sales of comparable properties and the opinions of fair value prepared by
independent real estate appraisers. Long-lived assets to be disposed of are
reported at the lower of carrying amount or fair value less cost to sell.

INCOME TAXES: No provision has been made for federal or state income taxes on
partnership net income, since the partnership is not subject to income tax.
Partnership income is includable in the taxable income of the individual
partners as required under applicable income tax laws. Certain items, primarily
related to depreciation methods, are accounted for differently for income tax
reporting purposes (see Note 6).



                                       13
<PAGE>   14

DEL TACO INCOME PROPERTIES IV
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999



NOTE 1 - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CONTINUED

NET INCOME PER LIMITED PARTNERSHIP UNIT: Net income per limited partnership unit
is calculated based upon 165,375, 165,415 and 165,415 weighted average units
outstanding in 1999, 1998 and 1997, respectively.

USE OF ESTIMATES: The preparation of the financial statements in conformity with
generally accepted accounting principles requires management to make certain
estimates and assumptions that affect the reported amounts of assets and
liabilities at the date of the financial statements and the reported amounts of
revenues and expenses during the reporting period. Actual results could differ
from those estimates.

NOTE 2 - PARTNERS' EQUITY

Pursuant to the partnership agreement, annual partnership net income or loss is
allocated one percent to the General Partner and 99 percent to the limited
partners. Partnership gains from any sale or refinancing will be allocated one
percent to the General Partner and 99 percent to the limited partners until
allocated gains and profits equal losses, distributions and syndication costs,
and until each class of limited partners receive their priority return as
defined in the partnership agreement. Additional gains will be allocated 12
percent to the General Partner and 88 percent to the limited partners.

NOTE 3 - SITE SELECTION AND DEVELOPMENT FEE

Under terms of the partnership agreement, the General Partner is entitled to
receive a fee in an amount equal to five percent of the gross proceeds of the
offering. The fee shall be for services rendered in connection with site
selection and the design and supervision of construction of improvements to
acquired properties. One percent of the gross proceeds of the offering has been
paid to the General Partner. The remaining four percent of this fee shall be
earned at the time the services are rendered, but shall not be paid and shall be
subordinated to the limited partners' interests until all restaurants have
opened and the limited partners have received certain minimum returns on their
investment, as required by the partnership agreement. It is the policy of the
partnership to accrue the site selection and development fee as an obligation to
the General Partner. No fees were earned for such services during 1999, 1998 and
1997.

Effective January 1, 1999, the special limited partners' (who resigned on May
19, 1998) 40 limited partnership units were redeemed by the Partnership.
Pursuant to the Partnership agreement, the redemption was completed at no cost
to the Partnership.




                                       14
<PAGE>   15


DEL TACO INCOME PROPERTIES IV
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999


NOTE 4 - LEASING ACTIVITIES

The partnership leases certain properties for operation of restaurants to Del
Taco, Inc. on a triple net basis. The leases are for terms of 32 years
commencing with the completion of the restaurant facility located on each
property and require monthly rentals equal to 12 percent of the gross sales of
the restaurants. Supplemental rent (as defined in the partnership agreement) may
be earned if certain criteria are met. There is no minimum rental under any of
the leases. The partnership had a total of three properties leased to Del Taco
as of December 31, 1999, 1998 and 1997 (Del Taco, in turn, has subleased one of
the restaurants to a Del Taco franchisee).

The two restaurants operated by Del Taco, for which the partnership is the
lessor, had combined, unaudited sales of $1,701,670, $1,697,771 and $1,523,099
and unaudited net income of $114,916, $107,870 and $76,600 for the years ended
December 31, 1999, 1998 and 1997, respectively. Net income by restaurant
includes charges for general and administrative expenses incurred in connection
with supervision of restaurant operations and interest expense. The one
restaurant operated by a Del Taco franchisee, for which the partnership is the
lessor, had unaudited sales of $940,462, $970,008 and $874,554 for the years
ended December 31, 1999, 1998 and 1997, respectively.

The Highland Avenue restaurant in Highland (San Bernardino), California had
unaudited net income of $5,073 and $7,339 and a net loss of $4,311 for the years
ended December 31, 1999, 1998 and 1997, respectively.

NOTE 5 - RELATED PARTIES

The receivable from Del Taco consists of rent accrued for the month of December
1999 as well as supplemental rent. These amounts were collected on January 17,
2000.

The General Partner received $3,611 in distributions relating to its one percent
interest in the partnership for the year ended December 31, 1999.

Del Taco, Inc. serves in the capacity of General Partner in other partnerships
which are engaged in the business of operating restaurants, and three other
partnerships which were formed for the purpose of acquiring real property in
California for construction of Mexican-American restaurants for lease under
long-term agreements to Del Taco, Inc. for operation under the Del Taco trade
name.



                                       15
<PAGE>   16

DEL TACO INCOME PROPERTIES IV
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999


NOTE 6 - INCOME TAXES

A reconciliation of financial statement net income to taxable income for each of
the periods is as follows:


<TABLE>
<CAPTION>
                                                 1999                 1998               1997
                                               --------            --------            --------
<S>                                            <C>                 <C>                 <C>
Net income per financial statements            $258,596            $254,610            $187,583
Excess book depreciation                         63,024              63,144              48,537
                                               --------            --------            --------
Taxable income                                 $321,620            $317,754            $236,120
                                               ========            ========            ========
</TABLE>


A reconciliation of partnership equity per the financial statements to net worth
for tax purposes as of December 31, 1999, is as follows:


<TABLE>
<S>                                            <C>
Partners' equity per financial
  statements                                    $2,034,296

Issue costs of limited partnership
  units capitalized for tax purposes               579,259

Excess book depreciation                           136,135
                                                ----------
Net worth for tax purposes                      $2,749,690
                                                ==========
</TABLE>



                                       16
<PAGE>   17


DEL TACO INCOME PROPERTIES IV
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999


NOTE 7 - CASH DISTRIBUTIONS TO LIMITED PARTNERS

Cash distributions paid to limited partners for the three years ended December
31, 1999 were as follows:


<TABLE>
<CAPTION>
                                           Cash                Weighted               Number of Units
                                      Distributions          Average Number            Outstanding at
                                       per Limited             of Units                  the End of
Quarter Ended                       Partnership Unit          Outstanding                 Quarter
                                   -------------------       --------------           ---------------
<S>                                    <C>                     <C>                       <C>
December 31, 1996                       $   0.41                165,415                   165,415
March 31, 1997                              0.49                165,415                   165,415
June 30, 1997                               0.37                165,415                   165,415
September 30, 1997                          0.43                165,415                   165,415
                                        --------
   Total paid in 1997                   $   1.70
                                        ========
December 31, 1997                       $   0.41                165,415                   165,415
March 31, 1998                              0.53                165,415                   165,415
June 30, 1998                               0.41                165,415                   165,415
September 30, 1998                          0.48                165,415                   165,415
                                        --------
   Total paid in 1998                   $   1.83
                                        ========
December 31, 1998                           0.47                165,375                   165,375
March 31, 1999                              0.85                165,375                   165,375
June 30, 1999                               0.39                165,375                   165,375
September 30, 1999                          0.45                165,375                   165,375
                                        --------
   Total paid in 1999                   $   2.16
                                        ========
</TABLE>


Cash distributions per limited partnership unit were calculated based upon the
weighted average number of units outstanding for each quarter and were paid from
operations. Cash distributions for the quarter ended December 31, 1999 amounted
to $.45 per limited partnership unit and were paid January 28, 2000.



                                       17
<PAGE>   18

                                    PART III


ITEM 9. DISAGREEMENTS ON ACCOUNTING AND FINANCIAL DISCLOSURE

None

ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF THE PARTNERSHIP'S GENERAL PARTNER

(a) & (b) The executive officers and directors of the General Partner and their
ages are set forth below:


<TABLE>
<CAPTION>
Name                         Title                                                                 Age
----                         -----                                                                 ---
<S>                         <C>                                                                   <C>
Kevin K. Moriarty            Director, Chairman and Chief Executive Officer                        53

C. Ronald Petty              President                                                             55

Paul W. Hitzelberger         Executive Vice President, Brand Strategy and
                                Franchise Relations/Development                                    55

Robert J. Terrano            Executive Vice President and
                                Chief Financial Officer                                            44

James D. Stoops              Executive Vice President, Operations                                  47

Janet D. Simmons             Senior Vice President, Purchasing                                     43

Michael L. Annis             Vice President, Secretary and General Counsel                         53

C. Douglas Mitchell          Vice President and Corporate Controller                               49

Timothy A. Hackbardt         Vice President, Marketing                                             36

Shirlene Lopez               Vice President, Corporate Development                                 35
</TABLE>

The above referenced executive officers and directors of the General Partner
will hold office until the annual meeting of its shareholders and directors,
which is scheduled for the later part of 2000.

(c)      None

(d)      No family relationship exists between any such director or executive
         officer of the General Partner.

(e)      The following is an account of the business experience during the past
         five years of each such director and executive officer:



                                       18
<PAGE>   19


Kevin K. Moriarty, Director, Chairman and Chief Executive Officer of Del Taco,
Inc. Mr. Moriarty began his career with Burger King Corporation in 1974 in
Operations Unit Management. In 1983, he was promoted to Area Manager in New
York, and was subsequently promoted to the Regional Vice President, Chicago
Region in 1985. In 1988, he became Executive Vice President and General Manager
of the North Central Division. Mr. Moriarty served in that position until 1990
when he joined Del Taco, Inc. as President and Chief Executive Officer on July
31, 1990. Mr. Moriarty has served as a Director of the General Partner since
1990.

C. Ronald Petty, President of Del Taco, Inc. Mr. Petty began his career in the
restaurant business in 1973 with McDonald's Corporation. He was employed by
McDonald's in a real estate capacity until 1978. For the next 12 years, Mr.
Petty was in various officer positions with Burger King. These positions
included Vice President of Real Estate, Sr. Vice President of Development,
Region Vice President, Sr. Vice President European Operations, President of
International and President of U.S. Mr. Petty served as President of Miami Subs
from 1990-1992; President and CEO of Denny's 1993-1996; President and CEO of
Peter Piper Pizza 1996-1998; President of Del Taco December 1998-present.

Paul W. Hitzelberger, Executive Vice President, Brand Strategy and Franchise
Relations/Development of Del Taco, Inc. He was appointed to his current position
in December 1995. Mr. Hitzelberger has responsibility for franchise development,
relations and training. He also oversees public relations and training for the
corporation. From 1991 to 1995, Mr. Hitzelberger was Executive Vice President,
Marketing of Del Taco, Inc. From September 1988 through September 1989, Mr.
Hitzelberger was Chief Executive Officer of Environmental Marketing Group. Prior
to that, Mr. Hitzelberger was a Vice President of Del Taco, Inc. Prior to
joining Del Taco, Inc., he served as Vice President - Marketing at the
department store division of Lucky Stores, Inc., a major supermarket retailer.
Mr. Hitzelberger received a Master of Business Administration degree from Loyola
University in Chicago, Illinois.

Robert J. Terrano, Executive Vice President and Chief Financial Officer of Del
Taco, Inc. From May 1994 to April 1995, Mr. Terrano served as Chief Financial
Officer for Denny's, Inc. in Spartanburg, S.C. From August 1983 to May 1994, he
served with Burger King Corporation, Miami Florida, in a variety of positions,
most recently as Division Controller. Mr. Terrano joined Del Taco, Inc. in April
1995.

James D. Stoops, Executive Vice President, Operations of Del Taco, Inc. From
1968 to 1991, Mr. Stoops served in a wide variety of Operations positions with
Burger King Corporation with increasing levels of responsibility. In 1985, Mr.
Stoops was appointed Region Vice President/General Manager for the New York
region and served in that position until October of 1990. In January of 1991, he
joined Del Taco, Inc. in his current post.

Janet D. Simmons, Senior Vice President, Purchasing of Del Taco, Inc. From 1979
to 1986, Ms. Simmons was with Denny's Inc. She served in the Research and
Development department in a variety of positions until 1982 when she was
promoted to the position of Purchasing Agent. Ms. Simmons was hired in 1986 as
Manager of Contract Purchasing with Carl Karcher Enterprises, a post she held
until March 1990 when she became Vice President, Purchasing for Del Taco, Inc.
Ms. Simmons has a Bachelor of Science degree in Foods and Nutrition from Cal
State Polytechnic University in Pomona, California.



                                       19
<PAGE>   20


Michael L. Annis, Vice President, Secretary and General Counsel of Del Taco,
Inc. From 1981 to 1986 Mr. Annis served as Regional Real Estate Manager and
Director of Real Estate Services with Taco Bell, Inc. In 1986 he served as
Regional General Manager with Quaker State Minit Lube. In January of 1987 Mr.
Annis joined Red Robin International, Inc. as General Counsel and was
subsequently promoted to Vice President/Secretary and later Vice President Real
Estate Development/Secretary and General Counsel, the position he held until
joining Del Taco, Inc. in December of 1993. Mr. Annis received his J.D. Degree
from Whittier College.

C. Douglas Mitchell, Vice President and Corporate Controller. Mr. Mitchell
joined Del Taco, Inc. in August of 1994 as Controller and was promoted to his
current position in January 1996. From 1990 to 1994, Mr. Mitchell was a Senior
Audit Manager with Coopers & Lybrand. Prior to 1990, Mr. Mitchell held various
positions in finance and accounting with the Geneva Companies (a subsidiary of
Chemical Bank), Zaremba Corporation (a real estate developer) and The Dexter
Corporation (an international manufacturer of specialty materials). Mr. Mitchell
has a Bachelor of Science degree with a major in accounting from the University
of Southern California.

Timothy A. Hackbardt, Vice President, Marketing of Del Taco, Inc. Mr. Hackbardt
joined Del Taco, Inc. in November 1999. Prior to then, since November of 1995,
he served as Vice President of Marketing of Taco Time International, Inc.,
Eugene, OR. From September 1994 to November 1995, Mr. Hackbardt was Director of
Marketing for Wok Spirit Chinese Delivery restaurants in Newport Beach, CA. From
December 1992 to September 1994, Mr. Hackbardt was Director of Marketing for
Fosters Freeze International, Inc., San Luis Obispo, CA. Prior to then, Mr.
Hackbardt held various positions in the television and radio industry in sales
and sales management. Mr. Hackbardt is a graduate of Central Michigan University
where he received a Bachelor of Applied Arts, majoring in Broadcast and
Cinematic Arts and minoring in Marketing.

Shirlene Lopez, Vice President, Corporate Development & Design of Del Taco, Inc.
Ms. Lopez began her career with Del Taco in 1978 as an hourly employee and
advanced through the ranks to General Manager in 1984. Ms. Lopez was promoted to
the corporate office in 1989 as Human Resource Manager. In 1994, she was
promoted to Executive Project Manager reporting to the CEO and in 1996, to
Director of Corporate Development in charge of all interior image and design.
Ms. Lopez has held her current position since August 1997.

ITEM 11. MANAGEMENT REMUNERATION AND TRANSACTIONS

The partnership has no executive officers or directors and pays no direct
remuneration to any executive officer or director of its General Partner. The
partnership has not issued any options or stock appreciation rights to any
executive officer or director of its General Partner, nor does the partnership
propose to pay any annuity, pension or retirement benefits to any executive
officer or director of its General Partner. The partnership has no plan, nor
does the partnership presently propose a plan, which will result in any
remuneration being paid to any executive officer or director of the General
Partner upon termination of employment.

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

(a)      No person of record currently owns more than five percent of limited
         partnership units of the partnership, nor was any person known of by
         the partnership to own of record and beneficially, or beneficially
         only, more than five percent of such securities.

(b)      Neither Del Taco, Inc., nor any executive officer or director of Del
         Taco, Inc. owns any limited partnership units of the partnership.




                                       20
<PAGE>   21

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT -
(Continued)

(c)      The partnership knows of no contractual arrangements, the operation or
         the terms of which may at a subsequent date result in a change in
         control of the partnership, except for provisions in the partnership
         agreement providing for removal of the General Partner by holders of a
         majority of the limited partnership units and if a material event of
         default occurs under the financing agreements of the General Partner.

ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

(a)      No transactions have occurred between the partnership and any executive
         officer or director of its General Partner.

         During 1999, the following transactions occurred between the
         partnership and the General Partner pursuant to the terms of the
         partnership agreement.

         (1)      The General Partner earned $2,586 as its one percent share of
                  the net income of the partnership.

         (2)      The General Partner received $3,611 in distributions relating
                  to its one percent interest in the partnership.

(b)      During 1999, the partnership had no business relationships with any
         entity of a type required to be reported under this item.

(c)      Neither the General Partner, any director or officer of the General
         Partner or any associate of any such person, was indebted to the
         partnership at any time during 1999 for any amount in excess of
         $60,000.

(d)      Not applicable.



                                       21
<PAGE>   22

                                     PART IV



ITEM 14(A)(1) AND (2). EXHIBITS, FINANCIAL STATEMENTS SCHEDULES, AND REPORTS ON
FORM 8-K

         Financial statement schedules:

                  Schedule III - Real Estate and Accumulated Depreciation

         Financial statement schedules other than those referred to above have
         been omitted because they are not applicable or not required.

(b)      No reports on Form 8-K were filed during the last quarter of 1999.

(c)      Exhibits required by Item 601 of Regulation S-K:

         1.       Incorporated herein by reference, Restated Agreement of
                  Limited Partnership of Del Taco Income Properties IV filed as
                  Exhibit 3.01 to Partnership's Registration Statement on Form
                  S-11 as filed with the Securities and Exchange Commission on
                  June 5, 1987.

         2.       Incorporated herein by reference, Amendment to Restated
                  Agreement of Limited Partnership of Del Taco Income Properties
                  IV.

         3.       Incorporated herein by reference, Form of Standard Lease to be
                  entered into by Partnership and Del Taco, Inc., as lessee,
                  filed as Exhibit 10.02 to Partnership's Registration Statement
                  on Form S-11 as filed with the Securities and Exchange
                  Commission on June 5, 1987.





                                       22
<PAGE>   23

                  DEL TACO INCOME PROPERTIES IV - SCHEDULE III
                    REAL ESTATE AND ACCUMULATED DEPRECIATION

                                DECEMBER 31, 1999



<TABLE>
<CAPTION>
                                                                                              Cost capitalized     Gross amount at
                                                              Initial cost                      subsequent to      which carried at
                                                               to company                        acquisition        close of period
                                                    --------------------------------------------------------------------------------
    Description                                         Land              Buildings &                             Land, buildings &
(All Restaurants)                                      & land               improve-              Carrying            improvements
                              Encumbrances          improvements              ments                 costs                 Total
------------------------------------------------------------------------------------------------------------------------------------
<S>                           <C>                   <C>                   <C>                   <C>                   <C>
Placentia, CA                 $       --            $  465,933            $  485,961            $       --            $  951,894
Lake Elsinore, CA                     --               449,058               468,361                    --               917,419
San Bernardino, CA                    --               321,709               335,538                    --               657,247
                              ------------------------------------------------------------------------------------------------------
                                      --            $1,236,700            $1,289,860            $       --            $2,526,560
                              ======================================================================================================

<CAPTION>

                                                                                         Life on which
                                                                                     depreciation in latest
    Description              Accumulated           Date of              Date             income statement
(All Restaurants)            depreciation        construction         acquired             is computed
-----------------------------------------------------------------------------------------------------------
<S>                          <C>                    <C>            <C>                   <C>
Placentia, CA                $  204,983             1988                  1988            20(LI), 35(BI)
Lake Elsinore, CA               197,560             1989                  1989            20(LI), 35(BI)
San Bernardino, CA              141,530             1989                  1989            20(LI), 35(BI)
                             ----------
                             $  544,073
                             ==========
</TABLE>


<TABLE>
<CAPTION>
                                                                Accumulated
                                         Restaurants           depreciation
                                         -----------           ------------
<S>                                       <C>                   <C>
Balances at December 31, 1996:            $2,526,560            $  378,269
   Acquisitions                                   --                55,268
   Sales                                          --                    --
                                          ----------            ----------
Balances at December 31, 1997:             2,526,560               433,537
   Acquisitions                                   --                55,268
   Sales                                          --                    --
                                          ----------            ----------
Balances at December 31, 1998:             2,526,560               488,805
   Acquisitions                                   --                55,268
   Sales                                          --                    --
                                          ----------            ----------
Balances at December 31, 1999:            $2,526,560            $  544,073
                                          ==========            ==========
</TABLE>



                                       23
<PAGE>   24

                                   SIGNATURES


Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the partnership has duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized.



                                             DEL TACO INCOME PROPERTIES IV
                                             a California limited partnership

                                             Del Taco, Inc.
                                             General Partner



Date March 07, 2000                          Kevin K. Moriarty
     --------------                          --------------------------------
                                             Kevin K. Moriarty
                                             Director, Chairman and Chief
                                             Executive Officer



Date March 07, 2000                          Michael L. Annis
     --------------                          --------------------------------
                                             Michael L. Annis
                                             Vice President, Secretary and
                                             General Counsel




Date March 07, 2000                          Robert J. Terrano
     --------------                          ------------------------------
                                             Robert J. Terrano
                                             Executive Vice President and
                                             Chief Financial Officer




Date March 07, 2000                          C. Douglas Mitchell
     --------------                          --------------------------------
                                             C. Douglas Mitchell
                                             Vice President and Corporate
                                             Controller




                                       24
<PAGE>   25


                                  EXHIBIT INDEX

<TABLE>
Exhibit             Description
-------             -----------
<S>                 <C>
27                  Financial Data Schedule
</TABLE>