<PAGE>
 
                                 EXHIBIT 10.4

                                   EXHIBIT C


                         REGISTRATION RIGHTS AGREEMENT

     THIS REGISTRATION RIGHTS AGREEMENT (this "Agreement"), dated as of December
3, 1997, by and between Rentech, Inc., a corporation organized under the laws of
the State of Colorado, U.S.A., with headquarters located at 1331 17th Street,
Suite 720, Denver, Colorado 80202 (the "Company"), and the buyer set forth on
the execution page hereof (the "Buyer").

                                    RECITALS

     A.   In connection with the Securities Purchase Agreement by and between
the parties of even date herewith (the "Securities Purchase Agreement"), the
Company has agreed, upon the terms and subject to the conditions of the
Securities Purchase Agreement, to issue and sell to the Buyer (i) a number of
shares of the Company's Series 1997-B Convertible Preferred Stock of Rentech,
Inc. (the "Series B Shares") and (ii) a number of shares of the Company's Series
1997-C Convertible Preferred Stock of Rentech, Inc. (the "Series C Shares"). The
Series B Shares and the Series C Shares (collectively, the "Preferred Shares")
are each convertible in accordance with the terms of the Articles of Amendment
(as defined in the Securities Purchase Agreement) into common stock of the
Company, no par value per share ("Common Stock"). The Common Stock into which
the Preferred Shares are convertible may be referred to herein as the
"Conversion Shares." In accordance with the terms of the Articles of Amendment,
shares of Common Stock may be issued in payment of dividends ("Dividend
Shares").

     B.   To induce the Buyer to execute and deliver the Securities Purchase
Agreement, the Company has agreed to provide certain registration rights under
the Securities Act of 1933, as amended, and the rules and regulations
thereunder, or any similar successor statute (collectively, the "1933 Act"), and
applicable state securities laws.

                                  AGREEMENTS

     NOW THEREFORE, in consideration of the premises and the mutual covenants
contained herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged by all parties hereto, the Company
and the Buyer hereby agree as follows:

     1.   DEFINITIONS.

     a.   As used in this Agreement, the following terms shall have the
following meanings:

          i.   "Investor" or "Investors" means the Buyer and any permitted
          transferee(s) or assignee(s) thereof to whom the Buyer assigns this
          Agreement and who agrees to become bound by the provisions of this
          Agreement in accordance with Section 9 hereof.
 
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          ii.  "Register," "registered," and "registration" refer to a
          registration effected by preparing and filing a Registration Statement
          or Statements in compliance with the 1933 Act and pursuant to Rule 415
          under the 1933 Act or any successor rule providing for offering
          securities on a continuous basis ("Rule 415"), and the declaration or
          ordering of effectiveness of such Registration Statement by the United
          States Securities and Exchange Commission (the "SEC").
 
          iii. "Registrable Securities" means the Conversion Shares and the
          Dividend Shares (if any), and any shares of capital stock issued or
          issuable, from time to time (with any adjustments) on or in exchange
          for or otherwise with respect to either of the foregoing (including
          without limitation any shares issued pursuant to Section 2(b)
          hereinafter).
 
          iv.  "Registration Statement" or "Registration Statements" means a
     registration statement or statements of the Company filed under the 1933
     Act.

     b.   Capitalized terms used herein and not otherwise defined herein shall
have the respective meanings set forth in the Securities Purchase Agreement.

     2.   REGISTRATION.

     a.   Mandatory Registration.  The Company shall use its best efforts to
          ----------------------                                            
prepare, and, on or before sixty (60) days after the date of the First Closing,
file with the SEC a Registration Statement or Registration Statements (as
necessary) on Form S-3 (or, if such form is unavailable for such a registration,
on such other form as is available for such a registration of all of the
Registrable Securities) (any of which may contain a combined prospectus with
other registrations by the Company), covering the resale of all of the
Registrable Securities, which Registration Statement(s), to the extent allowable
under the 1933 Act and the rules promulgated thereunder (including without
limitation Rule 416), shall state that such Registration Statement(s) also
covers such indeterminate number of additional shares of Common Stock as may
become issuable upon conversion of the Preferred Shares to prevent dilution
resulting from stock splits, stock dividends or similar transactions. A copy of
the Registration Statement(s) (and each amendment or supplement thereto, and
each request for acceleration of effectiveness thereof) shall be provided to
(and subject to the approval of the Buyer, which approval shall not be
unreasonably withheld or denied) the Buyer and its counsel prior to its filing
or other submission.

     b.   Liquidated Damages.  The Company shall use its best efforts to obtain
          ------------------                                                   
effectiveness of the Registration Statement as soon as practicable. If (i) the
Registration Statement(s) covering the Registrable Securities required to be
filed by the Company pursuant to Section 2(a) hereof is not declared effective
by the SEC within ninety (90) days after the date of the First Closing (other
than by reason of any act or failure to act in a timely manner by the Investors
or their counsel) (the "Registration Deadline") or if, after the Registration
Statement has been declared effective by the SEC, sales cannot be made pursuant
to the Registration Statement (by reason of stop order, the Company's failure to
update the Registration Statement, or any other reason outside the control of
the Investors), or (ii) the Common Stock is not listed or included for quotation
on the National Association of Securities Dealers Automated Quotation system
Small Cap Market ("NASDAQ Small Cap"), or another United States national
exchange,

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then the Company will make payments to the Investors, as liquidated damages and
in such amounts and at such times as shall be determined pursuant to this
Section 2(b) as partial relief for the damages to the Investors by reason of any
such delay in or reduction of their ability to sell the Registrable Securities
(which remedy shall not be exclusive of any other remedies available at law or
in equity), an amount to be determined as follows. The Company shall pay to the
Investor an amount equal to the purchase price for the Series B Shares purchased
at the First Closing (including, without limitation, any Preferred Shares that
have been converted into Conversion Shares then held by such Investors) (the
"Aggregate Share Price") multiplied by two and one-half hundredths (.025) times
the sum of: (i) the number of months (prorated for partial months) beginning the
day after the Registration Deadline and ending on the date the Registration
Statement is declared effective by the SEC, provided, however, that there shall
be excluded from such period any delays which are solely attributable to changes
required by the Investors in the Registration Statement with respect to
information relating to the Investors, including, without limitation, changes to
the plan of distribution, or to the failure of the Investors to conduct their
review of the registration statement pursuant to Section 2(a) above in a
reasonably prompt manner; (ii) the number of months (prorated for partial
months) that sales cannot be made pursuant to the Registration Statement after
the Registration Statement has been declared effective; and (iii) the number of
months (prorated for partial months) that the Common Stock is not listed or
included for quotation on  the NASDAQ Small Cap or another United States
national exchange after the Registration Statement has been declared effective.

     For example, if the Registration Statement becomes effective one (1) month
     -----------                                                               
after the end of such ninety (90) day period, the Company would pay US $12,500
for each US $500,000 of Aggregate Share Price and would continue to pay US
$12,500 for each US $500,000 of Aggregate Share Price until the Registration
Statement becomes effective.

     Such amounts shall be paid in cash or, at the Investor's option such
amounts may be convertible into Common Stock at the "Conversion Price" for the
Series B Shares, as defined in the Articles of Amendment. Any shares of Common
Stock issued upon conversion of such amounts shall be Registrable Securities. If
the Investor desires to convert the amounts due hereunder into Registrable
Securities it shall so notify the Company in writing within two (2) business
days of the date on which such amounts are first payable in cash and such
amounts shall be so convertible (pursuant to the mechanics set forth in the
Debentures), beginning on the last day upon which the cash amount would
otherwise be due in accordance with the following sentence. Payments of cash
pursuant hereto shall be made within five (5) days after the end of each period
that gives rise to such obligation, provided that, if any such period extends
for more than thirty (30) days, interim payments shall be made for the full
amount owed up to the date of such interim payment at the end of each thirty
(30) day period.

     c.   Piggy-Back Registrations.  If the Company has previously filed
          ------------------------                                      
(previous to the date of this Agreement), or at any time prior to the expiration
of the Registration Period (as hereinafter defined) the Company shall file with
the SEC a Registration Statement relating to an offering for its own account or
the account of others under the 1933 Act of any of its equity securities (other
than on Form S-4 or Form S-8 or their then equivalents relating to equity
securities to be issued solely in connection with any acquisition of any entity
or business or equity securities issuable in connection with stock option or
other employee benefit plans) the Company shall send to the Investor written
notice of such determination and, if within twenty (20) days after receipt of
such notice, such Investor shall so request in writing, the Company

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shall include in such Registration Statement all or any part of the Registrable
Securities such Investor requests to be registered, except that if, in
connection with any underwritten public offering for the account of the Company
the managing underwriter(s) thereof shall impose a limitation on the number of
shares of Common Stock which may be included in the Registration Statement
because, in such underwriter(s)' reasonable good faith judgment, marketing or
other factors dictate such limitation is necessary to facilitate public
distribution, then the Company shall be obligated to include in such
Registration Statement only such limited portion of the Registrable Securities
with respect to which such Investor has requested inclusion hereunder; provided
that no portion of the equity securities which the Company is offering for its
own account shall be excluded; provided, further that the Company shall be
entitled to exclude Registrable Securities to the extent necessary to avoid
breaching obligations existing prior to the date hereof to other stockholders of
the Company.

     Any exclusion of Registrable Securities shall be made pro rata among the
Investors seeking to include Registrable Securities, in proportion to the number
of Registrable Securities sought to be included by such Investors; provided,
however, that the Company shall not exclude any Registrable Securities unless
the Company has first excluded all outstanding securities, the holders of which
are not entitled to inclusion of such securities in such Registration Statement
or are not entitled to pro rata inclusion with the Registrable Securities; and
provided, further, however, that, after giving effect to the immediately
preceding proviso, any exclusion of Registrable Securities shall be made pro
rata with holders of other securities having the right to include such
securities in the Registration Statement other than holders of securities
entitled to inclusion of their securities in such Registration Statement by
reason of demand registration rights or whose registration rights existed prior
to the date hereof. No right to registration of Registrable Securities under
this Section 2(c) shall be construed to limit any registration required under
Section 2(a) hereof. If an offering in connection with which an Investor is
entitled to registration under this Section 2(c) is an underwritten offering,
then each Investor whose Registrable Securities are included in such
Registration Statement shall, unless otherwise agreed by the Company, offer and
sell such Registrable Securities in an underwritten offering using the same
underwriter or underwriters and, subject to the provisions of this Agreement, on
the same terms and conditions as other shares of Common Stock included in such
underwritten offering.

     NOTWITHSTANDING ANYTHING HEREIN TO THE CONTRARY, IF THE REGISTRABLE
SECURITIES ARE INCLUDED IN AND REGISTERED UNDER FORM S-1 NO. 333-40175, FILED
WITH THE SEC ON NOVEMBER 13, 1997 (THE "FORM S-1"), THEN TO THE EXTENT OF SUCH
INCLUSION AND REGISTRATION, NO REGISTRATION STATEMENT NEED BE FILED WITH RESPECT
TO SUCH REGISTRABLE SECURITIES INCLUDED IN AND REGISTERED UNDER THE FORM S-1,
AND THIS REGISTRATION RIGHTS AGREEMENT SHALL BE VOID WITH RESPECT TO SUCH
REGISTRABLE SECURITIES INCLUDED IN AND REGISTERED UNDER THE FORM S-1. THEREFORE,
IF ALL OF THE REGISTRABLE SECURITIES ARE INCLUDED IN AND REGISTERED UNDER THE
FORM S-1, NO REGISTRATION STATEMENT NEED BE FILED HEREUNDER.

     d.  Eligibility for Form S-3.  The Company represents and warrants that it
         ------------------------                                              
meets the requirements for the use of Form S-3 for registration of the sale by
the Buyer and any other Investor of the Registrable Securities and the Company
shall file all reports required to be filed by the Company with the SEC in a
timely manner so as to maintain such eligibility for the use of Form S-3. In the
event that Form S-3 is not available for registration of the Registrable
Securities, the Company shall register the securities on another appropriate
form.

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<PAGE>
 
     3.  RELATED OBLIGATIONS.  In connection with the registration of the
Registrable Securities, the Company shall have the following obligations:

     a.  The Company shall use its best efforts to cause such Registration
Statement(s) relating to Registrable Securities to become effective as soon as
possible after such filing, but in no event later than the Registration
Deadline, and keep the Registration Statement(s) effective pursuant to Rule 415
at all times until the earlier of (i) the date on which all of the Registrable
Securities have been sold (and no further Registrable Securities may be issued
in the future), (ii) the date as of which the Investors may immediately sell all
of the Registrable Securities without restriction pursuant to Rule 144
promulgated under the 1933 Act (or successor thereto) or otherwise, or (iii) the
date on which none of the Preferred Shares is outstanding (the "Registration
Period"), which Registration Statement(s) (including any amendments or
supplements thereto and prospectuses contained therein) shall not contain any
untrue statement of a material fact or omit to state a material fact required to
be stated therein, or necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading.

     b.  The Company shall prepare and file with the SEC such amendments
(including post-effective amendments) and supplements to the Registration
Statement and the prospectus used in connection with the Registration Statement
as may be necessary to keep the Registration Statement effective at all times
during the Registration Period, and, during such period, comply with the
provisions of the 1933 Act with respect to the disposition of all Registrable
Securities of the Company covered by the Registration Statement until such time
as all of such Registrable Securities shall have been disposed of in accordance
with the intended methods of disposition by the seller or sellers thereof as set
forth in the Registration Statement. In the event the number of shares available
under a Registration Statement filed pursuant to this Agreement is insufficient
to cover all of the Registrable Securities issued or issuable upon conversion of
the Preferred Shares, the Company shall amend the Registration Statement, or
file a new Registration Statement (on the short form available therefor, if
applicable), or both, so as to cover all of the Registrable Securities, in each
case, as soon as practicable, but in any event within fifteen (15) days after
the necessity therefor arises (based on the market price of the Common Stock and
other relevant factors on which the Company reasonably elects to rely). The
Company shall use its best efforts to cause such amendment and/or new
Registration Statement to become effective as soon as practicable following the
filing thereof.

     c.  The Company shall furnish to each Investor whose Registrable Securities
are included in the Registration Statement(s) promptly after the same is
prepared and publicly distributed, filed with the SEC, or received by the
Company, (i) one copy of the Registration Statement and any amendment thereto,
each preliminary prospectus and prospectus and each amendment or supplement
thereto in each case relating to such Registration Statement (other than any
portion thereof which contains information for which the Company has sought
confidential treatment) and, in the case of the Registration Statement referred
to in Section 2(a), each letter written by or on behalf of the Company to the
SEC or the staff of the SEC, and each item of correspondence from the SEC or the
staff of the SEC, in each case relating to such Registration Statement; and (ii)
such number of copies of a prospectus, including a preliminary prospectus, and
all amendments and supplements thereto and such other documents as such Investor
may reasonably request in order to facilitate the disposition of the Registrable
Securities owned (or to be owned) by such Investor.

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<PAGE>
 
     d.  The Company shall use reasonable efforts to (i) register and qualify
the Registrable Securities covered by the Registration Statement(s) under such
other securities or "blue sky" laws of such jurisdictions in the United States
as each Investor who holds (or has the right to hold) Registrable Securities
being offered reasonably requests, (ii) prepare and file in those jurisdictions
such amendments (including post-effective amendments) and supplements to such
registrations and qualifications as may be necessary to maintain the
effectiveness thereof during the Registration Period, (iii) take such other
actions as may be necessary to maintain such registrations and qualifications in
effect at all times during the Registration Period, and (iv) take all other
actions reasonably necessary or advisable to qualify the Registrable Securities
for sale in such jurisdictions; provided, however, that the Company shall not be
required in connection therewith or as a condition thereto to (a) qualify to do
business in any jurisdiction where it would not otherwise be required to qualify
but for this Section 3(d), (b) subject itself to general taxation in any such
jurisdiction, (c) file a general consent to service of process in any such
jurisdiction, (d) provide any undertakings that cause more than nominal expense
or burden to the Company, or (e) make any change in its charter or bylaws, which
in each case the Board of Directors of the Company determines to be contrary to
the best interests of the Company and its stockholders.

     e.  As promptly as practicable after becoming aware of such event, the
Company shall notify each Investor of the happening of any event, of which the
Company has knowledge, as a result of which the prospectus included in a
Registration Statement, as then in effect, includes an untrue statement of a
material fact or omission to state a material fact required to be stated therein
or necessary to make the statements therein, in light of the circumstances under
which they were made, not misleading, and use its best efforts promptly to
prepare a supplement or amendment to the Registration Statement to correct such
untrue statement or omission, and deliver such number of copies of such
supplement or amendment to each Investor as such Investor may reasonably
request.

     f.  The Company shall use its best efforts to prevent the issuance of any
stop order or other suspension of effectiveness of a Registration Statement,
and, if such an order is issued, to obtain the withdrawal of such order at the
earliest possible moment and to notify each Investor who holds Registrable
Securities being sold (or, in the event of an underwritten offering, the
managing underwriters) of the issuance of such order and the resolution thereof.

     g.  [Intentionally omitted.]

     h.  At the request of the Investor, but no more than two (2) times in any
one ninety (90) day period, the Company shall furnish, on the date of
effectiveness of the Registration Statement and thereafter from time to time on
such dates as the Investor may reasonably request (i) if required by an
underwriter, a letter, dated such date, from the Company's independent certified
public accountants in form and substance as is customarily given by independent
certified public accountants to underwriters in an underwritten public offering,
addressed to the underwriters, if any, and to the Investor; and (ii) an opinion,
dated as of such requested date, of counsel representing the Company for
purposes of such Registration Statement, in form, scope and substance as is
customarily given in an underwritten public offering, addressed to the
underwriters and the Investors.

     i.  The Company shall make available for inspection by (i) any Investor,
(ii) any underwriter participating in any disposition pursuant to a Registration
Statement, (iii) one firm of 

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attorneys and one firm of accountants or other agents retained by the Investors,
and (iv) one firm of attorneys retained by all such underwriters (collectively,
the "Inspectors") all pertinent financial and other records, and pertinent
corporate documents and properties of the Company (collectively, the "Records"),
as shall be reasonably deemed necessary by each Inspector to enable each
Inspector to exercise its due diligence responsibility, and cause the Company's
officers, directors and employees to supply all information which any Inspector
may reasonably request for purposes of such due diligence; provided, however,
that each Inspector shall hold in strict confidence and shall not make any
disclosure (except to an Investor) or use of any Record or other information
which the Company determines in good faith to be confidential, and of which
determination the Inspectors are so notified, unless (a) the disclosure of such
Records is necessary to avoid or correct a misstatement or omission in any
Registration Statement, (b) the release of such Records is ordered pursuant to a
final, non-appealable subpoena or order from a court or government body of
competent jurisdiction, or (c) the information in such Records has been made
generally available to the public other than by disclosure in violation of this
or any other agreement. The Company shall not be required to disclose any
confidential information in such Records to any Inspector until and unless such
Inspector shall have entered into confidentiality agreements (in form and
substance reasonably satisfactory to the Company) with the Company with respect
thereto, substantially in the form of this Section 3(i). Each Investor agrees
that it shall, upon learning that disclosure of such Records is sought in or by
a court or governmental body of competent jurisdiction or through other means,
give prompt notice to the Company and allow the Company, at its expense, to
undertake appropriate action to prevent disclosure of, or to obtain a protective
order for, the Records deemed confidential.

     j.  The Company shall hold in confidence and not make any disclosure of
information concerning an Investor provided to the Company unless (i) disclosure
of such information is necessary to comply with federal or state securities
laws, (ii) the disclosure of such information is necessary to avoid or correct a
misstatement or omission in any Registration Statement, (iii) the release of
such information is ordered pursuant to a subpoena or other final, non-
appealable order from a court or governmental body of competent jurisdiction, or
(iv) such information has been made generally available to the public other than
by disclosure in violation of this or any other agreement. The Company agrees
that it shall, upon learning that disclosure of such information concerning an
Investor is sought in or by a court or governmental body of competent
jurisdiction or through other means, give prompt notice to such Investor and
allow such Investor, at the Investor's expense, to undertake appropriate action
to prevent disclosure of, or to obtain a protective order for, such information.

     k.  The Company shall use its best efforts either to (i) cause all the
Registrable Securities covered by a Registration Statement to be listed on each
national securities exchange on which securities of the same class or series
issued by the Company are then listed, if any, if the listing of such
Registrable Securities is then permitted under the rules of such exchange, or
(ii) secure designation and quotation of all the Registrable Securities covered
by the Registration Statement on the NASDAQ Small Cap or, if, despite the
Company's best efforts to satisfy the preceding clause (i) or (ii), the Company
is unsuccessful in satisfying the preceding clause (i) or (ii), to secure the
inclusion for quotation on the OTC Bulletin Board for such Registrable
Securities.

     l.  The Company shall cooperate with the Investors who hold Registrable
Securities being offered and, to the extent applicable, any managing underwriter
or underwriters, to 

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facilitate the timely preparation and delivery of certificates (not bearing any
restrictive legend) representing the Registrable Securities to be offered
pursuant to a Registration Statement and enable such certificates to be in such
denominations or amounts, as the case may be, as the managing underwriter or
underwriters, if any, or, if there is no managing underwriter or underwriters,
the Investors may reasonably request and registered in such names as the
managing underwriter or underwriters, if any, or the Investors may request. Not
later than the date on which any Registration Statement registering the resale
of Registrable Securities is declared effective, the Company shall deliver (at
its expense) to its transfer agent instructions, accompanied by any required
opinion of counsel, that permit sales of unlegended securities in a timely
fashion that complies with then mandated securities settlement procedures for
regular way market transactions.

     m.  The Company shall provide a transfer agent and registrar, which may be
a single entity, for the Registrable Securities not later than the effective
date of the Registration Statement.

     n.  The Company shall comply with all applicable laws relating to a
Registration Statement and offering and sale of securities and all applicable
rules and regulations of governmental authorities in connection therewith
(including without limitation the 1933 Act and the Securities Exchange Act of
1934, as amended, and all the rules and regulations promulgated by the SEC).

     n.  The Company shall take all other reasonable actions necessary to
expedite and facilitate disposition by the Investors of Registrable Securities
pursuant to a Registration Statement.

     4.  OTHER OBLIGATIONS.  In connection with the registration of the
Registrable Securities, the Investors shall have the following obligations:

     a.  At least fifteen (15) days prior to the first anticipated filing date
of the Registration Statement, the Company shall notify each Investor of the
information the Company requires from each such Investor if such Investor elects
to have any of such Investor's Registrable Securities included in the
Registration Statement. It shall be a condition precedent to the obligations of
the Company to complete the registration pursuant to this Agreement with respect
to the Registrable Securities of a particular Investor that such Investor shall
furnish to the Company such information regarding itself, the Registrable
Securities held by it and the intended method of disposition of the Registrable
Securities held by it as shall be reasonably required to effect the registration
of such Registrable Securities and shall execute such documents in connection
with such registration as the Company may reasonably request.

     b.  Each Investor by such Investor's acceptance of the Registrable
Securities agrees to cooperate with the Company as reasonably requested by the
Company in connection with the preparation and filing of the Registration
Statement(s) hereunder, unless such Investor has notified the Company in writing
of such Investor's election to exclude all of such Investor's Registrable
Securities from the Registration Statement.

     c.  In the event Investors holding a majority of the Registrable Securities
being registered determine to engage the services of an underwriter, each
Investor agrees to enter into and perform such Investor's obligations under an
underwriting agreement, in usual and 

                                       8
<PAGE>
 
customary form, including, without limitation, customary indemnification and
contribution obligations, with the managing underwriter of such offering and
take such other actions as are reasonably required in order to expedite or
facilitate the disposition of the Registrable Securities, unless such Investor
notifies the Company in writing of such Investor's election to exclude all of
such Investor's Registrable Securities from the Registration Statement(s).

     d.  Each Investor agrees that, upon receipt of any notice from the Company
of the happening of any event of the kind described in Section 3(e) or 3(f),
such Investor will immediately discontinue disposition of Registrable Securities
pursuant to the Registration Statement(s) covering such Registrable Securities
until such Investor's receipt of the copies of the supplemented or amended
prospectus contemplated by Section 3(e) or 3(f) and, if so directed by the
Company, such Investor shall deliver to the Company (at the expense of the
Company) or destroy (and deliver to the Company a certificate of destruction)
all copies in such Investor's possession, of the prospectus covering such
Registrable Securities current at the time of receipt of such notice.

     e.  No investor may participate in any underwritten registration hereunder
unless such Investor (i) agrees to sell such Investor's Registrable Securities
on the basis provided in any underwriting arrangements approved by the Investors
entitled hereunder to approve such arrangements, (ii) completes and executes all
questionnaires, powers of attorney, indemnities, underwriting agreements and
other documents reasonably required under the terms of such underwriting
arrangements, and (iii) agrees to pay its pro rata share of all underwriting
discounts and commissions and any expenses in excess of those payable by the
Company pursuant to Section 5 below.

     5.  EXPENSES OF REGISTRATION.  The Company agrees to pay all reasonable
expenses, other than underwriting discounts and commissions, incurred in
connection with registrations, filings or qualifications pursuant to Sections 2
and 3, including, without limitation, all registration, listing and
qualifications fees, printers and accounting fees, and fees and disbursements of
counsel for the Company.

     6.  INDEMNIFICATION.  In the event any Registrable Securities are included
in a Registration Statement under this Agreement:

     a.  To the extent permitted by law, the Company will indemnify, hold
harmless and defend each Investor who holds such Registrable Securities, the
directors, officers and each person who controls any Investor within the meaning
of the 1933 Act or the Securities Exchange Act of 1934, as amended (the "1934
Act"), if any and any underwriter (as defined in the 1933 Act) for the
Investors, and the directors and the officers of, and each person, if any, who
controls, any such underwriter within the meaning of the 1933 Act or the 1934
Act (each, an "Indemnified Person"), against any losses, claims, damages,
liabilities or expenses (joint or several) (collectively, "Claims") to which any
of them may become subject insofar as such Claims (or actions or proceedings,
whether commenced or threatened, in respect thereof) arise out of or are based
upon: (i) any untrue statement or alleged untrue statement of a material fact in
a Registration Statement or the omission or alleged omission to state a material
fact therein required to be stated or necessary to make the statements therein
not misleading, (ii) any untrue statement or alleged untrue statement of a
material fact contained in any preliminary prospectus if used prior to the
effective date of such Registration Statement, or contained in the final

                                       9
<PAGE>
 
prospectus (as amended or supplemented, if the Company files any amendment
thereof or supplement thereto with the SEC) or the omission or alleged omission
to state therein any material fact necessary to make the statements made
therein, in light of the circumstances under which the statements therein were
made, not misleading, or (iii) any violation or alleged violation by the Company
of the 1933 Act, the 1934 Act, any other law, including, without limitation, any
state securities law, or any rule or regulation thereunder relating to the offer
or sale of the Registrable Securities pursuant to a Registration Statement (the
matters in the foregoing clauses (i) through (iii) being, collectively,
"Violations"). Subject to the restrictions set forth in Section 6(d) with
respect to the number of legal counsel, the Company shall reimburse the
Investors and each such underwriter or controlling person, promptly as such
expenses are incurred and are due and payable, for any legal fees or other
reasonable expenses incurred by them in connection with investigating or
defending any such Claim. Notwithstanding anything to the contrary contained
herein, the indemnification agreement contained in this Section 6(a): (i) shall
not apply to a Claim arising out of or based upon a Violation which occurs in
reliance upon and in conformity with information furnished in writing to the
Company by any Indemnified Person or underwriter for such Indemnified Person
expressly for use in connection with the preparation of the Registration
Statement or any such amendment thereof or supplement thereto, if such
prospectus was timely made available by the Company pursuant to Section 3(c)
hereof; (ii) with respect to any preliminary prospectus, shall not inure to the
benefit of any such person from whom the person asserting any such Claim
purchased the Registrable Securities that are the subject thereof (or to the
benefit of any person controlling such person) if the untrue statement or
omission of the material fact contained in the preliminary prospectus was
corrected in the prospectus, as then amended or supplemented, if such prospectus
was timely made available by the Company pursuant to Section 3(c) hereof; (iii)
shall not be available to the extent such Claim is based on a failure of the
Investor to deliver or to cause to be delivered the prospectus made available by
the Company; and (iv) shall not apply to amounts paid in settlement of any Claim
if such settlement is effected without the prior written consent of the Company,
which consent shall not be unreasonably withheld. Such indemnity shall remain in
full force and effect regardless of any investigation made by or on behalf of
the Indemnified Person and shall survive the transfer of the Registrable
Securities by the Investors pursuant to Section 9.

     b.  In connection with any Registration Statement in which an Investor is
participating, each such Investor agrees to indemnify, hold harmless and defend,
to the same extent and in the same manner as is set forth in Section 6(a), the
Company, each of its directors, each of its officers who signs the Registration
Statement, each person, if any, who controls the Company within the meaning of
the 1933 Act or the 1934 Act, any underwriter and any other stockholder selling
securities pursuant to the Registration Statement or any of its directors or
officers or any person who controls such stockholder or underwriter within the
meaning of the 1933 Act or the 1934 Act (collectively and together with an
Indemnified Person, an "Indemnified Party"), against any Claim to which any of
them may become subject, under the 1933 Act, the 1934 Act or otherwise, insofar
as such Claim arises out of or is based upon any Violation, in each case to the
extent (and only to the extent) that such violation occurs in reliance upon and
in conformity with written information furnished to the Company by such Investor
expressly for use in connection with such Registration Statement or to the
extent such Claim is based upon any violation or alleged violation by the
Investor of the 1933 Act, 1934 Act or any other law; and such Investor will
reimburse any legal or other expenses reasonably incurred by them in connection
with investigating or defending any such Claim; provided, however, that the
indemnity agreement contained in this Section 6(b) shall not apply to amounts
paid in settlement

                                       10
<PAGE>
 
of any Claim if such settlement is effected without the prior written consent of
such Investor, which consent shall not be unreasonably withheld; provided,
further, however, that the Investor shall be liable under this Section 6(b) for
only that amount of a Claim as does not exceed the net proceeds to such Investor
as a result of the sale of Registrable Securities pursuant to such Registration
Statement. Such indemnity shall remain in full force and effect regardless of
any investigation made by or on behalf of such Indemnified Party and shall
survive the transfer of the Registrable Securities by the Investors pursuant to
Section 9. Notwithstanding anything to the contrary contained herein, the
indemnification agreement contained in this Section 6(b) with respect to any
preliminary prospectus shall not inure to the benefit of any Indemnified Party
if the untrue statement or omission of material fact contained in the
preliminary prospectus was corrected on a timely basis in the prospectus, as
then amended or supplemented.

     c.  The Company shall be entitled to receive indemnities from underwriters,
selling brokers, dealer managers and similar securities industry professionals
participating in any distribution, to the same extent as provided above, with
respect to information such persons so furnished in writing by such persons
expressly for inclusion in the Registration Statement.

     d.  Promptly after receipt by an Indemnified Person or Indemnified Party
under this Section 6 of notice of the commencement of any action (including any
governmental action), such Indemnified Person or Indemnified Party shall, if a
Claim in respect thereof is to be made against any indemnifying party under this
Section 6, deliver to the indemnifying party a written notice of the
commencement thereof, and the indemnifying party shall have the right to
participate in, and, to the extent the indemnifying party so desires, jointly
with any other indemnifying party similarly noticed, to assume control of the
defense thereof with counsel mutually satisfactory to the indemnifying party and
the Indemnified Person or the Indemnified Party, as the case may be; provided,
however, that an Indemnified Person or Indemnified Party shall have the right to
retain its own counsel with the fees and expenses to be paid by the indemnifying
party, if, in the reasonable opinion of counsel retained by the indemnifying
party, the representation by such counsel of the Indemnified Person or
Indemnified Party and the indemnifying party would be inappropriate due to
actual or potential differing interests between such Indemnified Person or
Indemnified Party and any other party represented by such counsel in such
proceeding. The Company shall pay reasonable fees for only one separate legal
counsel for the Investors, and such legal counsel shall be selected by the
Investors holding a majority in interest of the Registrable Securities included
in the Registration Statement to which the Claim relates; provided, that legal
fees of such firm shall be reasonable. The failure to deliver written notice to
the indemnifying party within a reasonable time of the commencement of any such
action shall not relieve such indemnifying party of any liability to the
Indemnified Person or Indemnified Party under this Section 6, except to the
extent that the indemnifying party is prejudiced in its ability to defend
such action. The indemnification required by this Section 6 shall be made by
periodic payments of the amount thereof during the course of the investigation
or defense, as such expense, loss, damage or liability is incurred and is due
and payable.

     7.  CONTRIBUTION.  To the extent any indemnification by an indemnifying
party is prohibited or limited by law, the indemnifying party agrees to make the
maximum contribution with respect to any amounts for which it would otherwise be
liable under Section 6 to the fullest extent permitted by law; provided,
however, that (i) no contribution shall be made under circumstances where the
maker would not have been liable for indemnification under the fault standards
set forth in Section 6, (ii) no seller of Registrable Securities guilty of
fraudulent 

                                       11
<PAGE>
 
misrepresentation (within the meaning of Section 11(f) of the 1933 Act) shall be
entitled to contribution from any seller of Registrable Securities who was not
guilty of fraudulent misrepresentation, and (iii) contribution by any seller of
Registrable Securities shall be limited in amount to the net amount of proceeds
received by such seller from the sale of such Registrable Securities.

     8.  REPORTS UNDER THE 1934 ACT.  With a view to making available to the
Investors the benefits of Rule 144 promulgated under the 1933 Act or any other
similar rule or regulation of the SEC that may at any time permit the investors
to sell securities of the Company to the public without registration ("Rule
144"), the Company agrees to:

     a.  make and keep public information available, as those terms are
understood and defined in Rule 144;

     b.  file with the SEC in a timely manner all reports and other documents
required of the Company under the 1933 Act and the 1934 Act so long as the
Company remains subject to such requirements (it being understood that nothing
herein shall limit the Company's obligations under Section 4(c) of the
Securities Purchase Agreement) and the filing of such reports and other
documents is required for the applicable provisions of Rule 144; and

     c.  furnish to each Investor so long as such Investor owns Registrable
Securities, promptly upon request, (i) a written statement by the Company that
it has complied with the reporting requirements of Rule 144, the 1933 Act and
the 1934 Act, (ii) a copy of the most recent annual or quarterly report of the
Company and such other reports and documents so filed by the Company, and (iii)
such other information as may be reasonably requested to permit the investors to
sell such securities pursuant to Rule 144 without registration.

     9.  ASSIGNMENT OF REGISTRATION RIGHTS.  The rights to have the Company
register Registrable Securities pursuant to this Agreement shall be
automatically assignable by the Investors to any transferee of all or any
portion of Registrable Securities if: (i) the Investor agrees in writing with
the transferee or assignee to assign such rights, and a copy of such agreement
is furnished to the Company within a reasonable time after such assignment, (ii)
the Company is, within a reasonable time after such transfer or assignment,
furnished with written notice of (a) the name and address of such transferee or
assignee, and (b) the securities with respect to which such registration rights
are being transferred or assigned, (iii) immediately following such transfer or
assignment the further disposition of such securities by the transferee or
assignee is restricted under the 1933 Act and applicable state securities laws,
(iv) at or before the time the Company receives the written notice contemplated
by clause (ii) of this sentence the transferee or assignee agrees in writing
with the Company to be bound by all of the provisions contained herein, (v) such
transfer shall have been made in accordance with the applicable requirements of
the Securities Purchase Agreement, (vi) such transferee shall be an "accredited
investor" as that term defined in Rule 501 of Regulation D promulgated under the
1933 Act; and (vii) in the event the assignment occurs subsequent to the date of
effectiveness of the Registration Statement required to be filed pursuant to
Section 2(a), the transferee agrees to pay all reasonable expenses of amending
or supplementing such Registration Statement to reflect such assignment.
Notwithstanding anything herein to the contrary, no assignment of the rights
represented by this Agreement shall be effective unless in compliance with any
applicable securities laws of any applicable jurisdiction.

                                       12
<PAGE>
 
     10.  AMENDMENT OF REGISTRATION RIGHTS.  Provisions of this Agreement may be
amended and the observance thereof may be waived (either generally or in a
particular instance and either retroactively or prospectively), only with the
written consent of the Company and Investors who hold a majority of the
Registrable Securities. Any amendment or waiver effected in accordance with this
Section 10 shall be binding upon each Investor and the Company.

     11.  MISCELLANEOUS.

     a.   A person or entity is deemed to be a holder of Registrable Securities
whenever such person or entity owns of record such Registrable Securities. If
the Company receives conflicting instructions, notices or elections from two or
more persons or entities with respect to the same Registrable Securities, the
Company shall act upon the basis of instructions, notice or election received
from the registered owner of such Registrable Securities.

     b.   Any notices required or permitted to be given under the terms of this
Agreement shall be sent by registered or certified mail, return receipt
requested, or delivered personally or by courier and shall be effective five
days after being placed in the mail, if mailed, or upon receipt, if delivered
personally or by courier or facsimile, in each case properly addressed to the
party to receive such notice. The addresses for such communications shall be:

  If to the Company:     Intercell Corporation
                         370 17th Street, Suite 3290
                         Denver, Colorado 80202
                         Telephone: 303-592-1010
                         Facsimile: 303-592-1054
                         Attention: Mr. Paul H. Metzinger, President & CEO

     If to the Buyer, at the address on the signature page of the Securities
Purchase Agreement. Each party shall provide written notice to the other party
of any change in address.

     c.   Failure of any party to exercise any right or remedy under this
Agreement or otherwise, or delay by a party in exercising such right or remedy,
shall not operate as a waiver thereof.

     d.   This Agreement shall be governed by and interpreted in accordance with
the laws of the State of Delaware without regard to the principles of conflict
of laws. If any provision of this Agreement shall be invalid of unenforceable in
any jurisdiction, such invalidity or unenforceability shall not affect the
validity or enforceability of the remainder of this Agreement in that
jurisdiction or the validity or enforceability of any provision of this
Agreement in any other jurisdiction. Service of process in any civil action
relating to or arising out of this Agreement (including also all Exhibits or
Addenda hereto) or the transaction(s) contemplated herein may be accomplished
via certified mail, return receipt requested, and the parties hereby irrevocably
acknowledge and agree that such service of process by certified mail at the
parties' respective addresses as noted in Section 11(b) above (or such other
address as the party being served shall have provided as required in Section
11(b)) shall be sufficient to subject the party being served thereby to personal
jurisdiction in the state of Colorado, U.S.A.

                                       13
<PAGE>
 
     e.   This Agreement, the Debentures, the Warrants, the Escrow Agreement and
the Securities Purchase Agreement (including all exhibits and addenda thereto)
constitute the entire agreement between the parties hereto with respect to the
subject matter hereof and thereof. There are no restrictions, promises,
warranties or undertakings, other than those set forth or referred to herein and
therein. This Agreement and the Securities Purchase Agreement supersede all
prior agreements and understandings among the parties hereto with respect to the
subject matter hereof and thereof.

     f.   Subject to the requirements of Section 9 hereof, this Agreement shall
inure to the benefit of and be binding upon the permitted successors and assigns
of each of the parties hereto.

     g.   The headings in this Agreement are for convenience of reference only
and shall not limit or otherwise affect the meaning hereof.

     h.   This Agreement may be executed in two or more identical counterparts,
each of which shall be deemed an original but all of which shall constitute one
and the same agreement. This Agreement, once executed by a party, may be
delivered to the other party hereto by facsimile transmission of the signature
page of this Agreement bearing the signature of the party so delivering this
Agreement to the Escrow Agent, with the original executed Agreement to be
delivered to the Escrow Agent via overnight delivery.

     i.   Each party shall do and perform, or cause to be done and performed,
all such further acts and things, and shall execute and deliver all such other
agreements, certificates, instruments and documents, as the other party may
reasonably request in order to carry out the intent and accomplish the purposes
of this Agreement and the consummation of the transactions contemplated hereby.

     IN WITNESS WHEREOF, the parties have caused this Registration Rights
Agreement to be duly executed as of day and year first above written.



                           [SIGNATURE PAGE FOLLOWS]

                                       14
<PAGE>
 
               [SIGNATURE PAGE TO REGISTRATION RIGHTS AGREEMENT
                            DATED DECEMBER 3, 1997]



                                     COMPANY:
 
                                     INTERCELL CORPORATION

                                     By   /s/ Paul H. Metzinger
                                       -----------------------------------------
                                              Paul H. Metzinger, President & CEO



                                     BUYER:

                                     THE AUGUSTINE FUND. L.P.

                                     By:  Augustine Capital Management, Inc.

                                     By   /s/ Thomas F. Duszinski
                                       -----------------------------------------
                                              (Signature of authorized officer)

 

                                              (Print name and title)

                                       15