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                                                                  Exhibit 4(nnn)

                              JANUS INVESTMENT FUND

                          INVESTMENT ADVISORY AGREEMENT

                                JANUS TWENTY FUND

      THIS INVESTMENT ADVISORY AGREEMENT (the "Agreement") is made this 1st day
of July, 2004, between JANUS INVESTMENT FUND, a Massachusetts business trust
(the "Trust"), and JANUS CAPITAL MANAGEMENT LLC, a Delaware limited liability
company ("JCM").

                              W I T N E S S E T H:

      WHEREAS, the Trust is registered as an open-end management investment
company under the Investment Company Act of 1940, as amended (the "1940 Act"),
and has registered its shares for public offering under the Securities Act of
1933, as amended (the "1933 Act"); and

      WHEREAS, the Trust is authorized to create separate funds, each with its
own separate investment portfolio of which the beneficial interests are
represented by a separate series of shares; one of such funds created by the
Trust being designated as the Janus Twenty Fund (the "Fund"); and

      WHEREAS, the Trust and JCM deem it mutually advantageous that JCM should
assist the Trustees and officers of the Trust in the management of the
securities portfolio of the Fund.

      NOW, THEREFORE, the parties agree as follows:

      1.    Appointment. The Trust hereby appoints JCM as investment adviser and
manager with respect to the Fund for the period and on the terms set forth in
this Agreement. JCM hereby accepts such appointment and agrees to render the
services herein set forth, for the compensation herein provided.

      2.    Investment Advisory Services. JCM shall furnish continuous advice
and recommendations to the Fund as to the acquisition, holding, or disposition
of any or all of the securities or other assets which the Fund may own or
contemplate acquiring from time to time. JCM shall give due consideration to the
investment policies and restrictions and the other statements concerning the
Fund in the Trust Instrument, bylaws, and registration statements under the 1940
Act and the 1933 Act, and to the provisions of the Internal Revenue Code, as
amended from time to time, applicable to the Fund as a regulated investment
company. In addition, JCM shall cause its officers to attend meetings and
furnish oral or written reports, as the Trust may reasonably require, in order
to keep the Trustees and appropriate officers of the Trust fully informed as to
the condition of the investment portfolio of the Fund, the investment
recommendations of JCM, and the investment considerations which have given rise
to those recommendations. JCM shall supervise the purchase and sale of
securities as directed by the appropriate officers of the Trust.

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      3.    Other Services. JCM is hereby authorized (to the extent the Trust
has not otherwise contracted) but not obligated (to the extent it so notifies
the Trustees at least 60 days in advance), to perform (or arrange for the
performance by affiliates of) the management and administrative services
necessary for the operation of the Fund. JCM is specifically authorized, on
behalf of the Trust, to conduct relations with custodians, depositories,
transfer and pricing agents, accountants, attorneys, underwriters, brokers and
dealers, corporate fiduciaries, insurance company separate accounts, insurers,
banks and such other persons in any such other capacity deemed by JCM to be
necessary or desirable. JCM shall generally monitor and report to the Fund's
officers the Fund's compliance with investment policies and restrictions as set
forth in the currently effective prospectus and statement of additional
information relating to the shares of the Fund under the 1933 Act. JCM shall
make reports to the Trustees of its performance of services hereunder upon
request therefor and furnish advice and recommendations with respect to such
other aspects of the business and affairs of the Fund as it shall determine to
be desirable. JCM is also authorized, subject to review by the Trustees, to
furnish such other services as JCM shall from time to time determine to be
necessary or useful to perform the services contemplated by this Agreement.

      4.    Obligations of Trust. The Trust shall have the following obligations
under this Agreement:

            (a)   to keep JCM continuously and fully informed as to the
                  composition of its investment portfolio and the nature of all
                  of its assets and liabilities from time to time;

            (b)   to furnish JCM with a certified copy of any financial
                  statement or report prepared for it by certified or
                  independent public accountants and with copies of any
                  financial statements or reports made to its shareholders or to
                  any governmental body or securities exchange;

            (c)   to furnish JCM with any further materials or information which
                  JCM may reasonably request to enable it to perform its
                  function under this Agreement; and

            (d)   to compensate JCM for its services and reimburse JCM for its
                  expenses incurred hereunder in accordance with the provisions
                  hereof.

      5.    Compensation. The Trust shall pay to JCM for its investment advisory
services a fee, calculated and payable for each day that this Agreement is in
effect, of 1/365 of 0.64% of the daily closing net asset value of the Fund
(1/366 of 0.64% of the daily closing net asset value of the Fund in a leap
year). The fee shall be paid monthly.

      6.    Expenses Borne by JCM. In addition to the expenses which JCM may
incur in the performance of its investment advisory functions under this
Agreement, and the expenses which it may expressly undertake to incur and pay
under other agreements with the Trust or

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otherwise, JCM shall incur and pay the following expenses relating to the Fund's
operations without reimbursement from the Fund:

            (a)   Reasonable compensation, fees and related expenses of the
                  Trust's officers and its Trustees, except for such Trustees
                  who are not "interested persons," as defined in the 1940 Act,
                  of JCM; and

            (b)   Rental of offices of the Trust.

      7.    Expenses Borne by the Trust. The Trust assumes and shall pay all
expenses incidental to its organization, operations and business not
specifically assumed or agreed to be paid by JCM pursuant to Sections 3 and 6
hereof, including, but not limited to, investment adviser fees; any
compensation, fees, or reimbursements which the Trust pays to its Trustees who
are not "interested persons," as defined in the 1940 Act, of JCM; compensation
of the Fund's custodian, transfer agent, registrar and dividend disbursing
agent; legal, accounting, audit and printing expenses; administrative, clerical,
recordkeeping and bookkeeping expenses; brokerage commissions and all other
expenses in connection with execution of portfolio transactions (including any
appropriate commissions paid to JCM or its affiliates for effecting exchange
listed, over-the-counter or other securities transactions); interest; all
federal, state and local taxes (including stamp, excise, income and franchise
taxes); costs of stock certificates and expenses of delivering such certificates
to purchasers thereof; expenses of local representation in Massachusetts;
expenses of shareholders' meetings and of preparing, printing and distributing
proxy statements, notices, and reports to shareholders; expenses of preparing
and filing reports and tax returns with federal and state regulatory
authorities; all expenses incurred in complying with all federal and state laws
and the laws of any foreign country applicable to the issue, offer, or sale of
shares of the Fund, including, but not limited to, all costs involved in the
registration or qualification of shares of the Fund for sale in any
jurisdiction, the costs of portfolio pricing services and compliance systems,
and all costs involved in preparing, printing and mailing prospectuses and
statements of additional information to Fund shareholders; and all fees, dues
and other expenses incurred by the Trust in connection with the membership of
the Trust in any trade association or other investment company organization.

      8.    Treatment of Investment Advice. The Trust shall treat the investment
advice and recommendations of JCM as being advisory only, and shall retain full
control over its own investment policies. However, the Trustees may delegate to
the appropriate officers of the Trust, or to a committee of the Trustees, the
power to authorize purchases, sales or other actions affecting the portfolio of
the Fund in the interim between meetings of the Trustees.

      9.    Termination. This Agreement may be terminated at any time, without
penalty, by the Trustees of the Trust, or by the shareholders of the Fund acting
by vote of at least a majority of its outstanding voting securities, provided in
either case that sixty (60) days advance written notice of termination be given
to JCM at its principal place of business. This Agreement may be terminated by
JCM at any time, without penalty, by giving sixty (60) days advance written
notice of termination to the Trust, addressed to its principal place of
business. The Trust agrees that, consistent with the terms of the Trust
Instrument, the Trust shall cease to use the name "Janus" in connection with the
Fund as soon as reasonably practicable following any termination of this
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Agreement if JCM does not continue to provide investment advice to the Fund
after such termination.

      10.   Assignment. This Agreement shall terminate automatically in the
event of any assignment of this Agreement.

      11.   Term. This Agreement shall continue in effect until July 1, 2005,
unless sooner terminated in accordance with its terms, and shall continue in
effect from year to year thereafter only so long as such continuance is
specifically approved at least annually by (a) the vote of a majority of the
Trustees of the Trust who are not parties hereto or interested persons of any
such party, cast in person at a meeting called for the purpose of voting on the
approval of the terms of such renewal, and (b) either the Trustees of the Trust
or the affirmative vote of a majority of the outstanding voting securities of
the Fund. The annual approvals provided for herein shall be effective to
continue this Agreement from year to year if given within a period beginning not
more than ninety (90) days prior to July 1 of each applicable year,
notwithstanding the fact that more than three hundred sixty-five (365) days may
have elapsed since the date on which such approval was last given.

      12.   Amendments. This Agreement may be amended by the parties only if
such amendment is specifically approved (i) by a majority of the Trustees,
including a majority of the Trustees who are not interested persons (as that
phrase is defined in Section 2(a)(19) of the 1940 Act) of any party to this
Agreement and, if required by applicable law, (ii) by the affirmative vote of a
majority of the outstanding voting securities of the Fund (as that phrase is
defined in Section 2(a)(42) of the 1940 Act).

      13.   Other Series. The Trustees shall determine the basis for making an
appropriate allocation of the Trust's expenses (other than those directly
attributable to the Fund) between the Fund and the other series of the Trust.

      14.   Limitation of Personal Liability. All the parties hereto acknowledge
and agree that all liabilities of the Trust arising, directly or indirectly,
under this Agreement, of any and every nature whatsoever, shall be satisfied
solely out of the assets of the Fund and that no Trustee, officer or holder of
shares of beneficial interest of the Trust shall be personally liable for any of
the foregoing liabilities. The Trust Instrument describes in detail the
respective responsibilities and limitations on liability of the Trustees,
officers and holders of shares of beneficial interest of the Trust.

      15.   Limitation of Liability of JCM. JCM shall not be liable for any
error of judgment or mistake of law or for any loss arising out of any
investment or for any act or omission taken with respect to the Trust, except
for willful misfeasance, bad faith or gross negligence in the performance of its
duties, or by reason of reckless disregard of its obligations and duties
hereunder and except to the extent otherwise provided by law. As used in this
Section 15, "JCM" shall include any affiliate of JCM performing services for the
Trust contemplated hereunder and directors, officers and employees of JCM and
such affiliates.
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      16.   Activities of JCM. The services of JCM to the Trust hereunder are
not to be deemed to be exclusive, and JCM and its affiliates are free to render
services to other parties. It is understood that trustees, officers and
shareholders of the Trust are or may become interested in JCM as directors,
officers and shareholders of JCM, that directors, officers, employees and
shareholders of JCM are or may become similarly interested in the Trust, and
that JCM may become interested in the Trust as a shareholder or otherwise.

      17.   Certain Definitions. The terms "vote of a majority of the
outstanding voting securities," "assignment" and "interested persons" when used
herein, shall have the respective meanings specified in the 1940 Act, as now in
effect or hereafter amended, and the rules and regulations thereunder, subject
to such orders, exemptions and interpretations as may be issued by the
Securities and Exchange Commission under said Act and as may be then in effect.

      18.   Governing Law. This Agreement shall be construed in accordance with
the laws of the State of Colorado (without giving effect to the conflicts of
laws principles thereof) and the 1940 Act. To the extent that the applicable
laws of the State of Colorado conflict with the applicable provisions of the
1940 Act, the latter shall control.

      This Agreement shall supercede all prior investment advisory agreements
entered into between JCM and the Trust, on behalf of the Fund.

      IN WITNESS WHEREOF, the parties have caused their duly authorized officers
to execute this Investment Advisory Agreement as of the date and year first
above written.

                                        JANUS CAPITAL MANAGEMENT LLC

                                        By: /s/ Loren M. Starr
                                            ------------------------------------
                                            Loren M. Starr, Chief Financial
                                            Officer and Senior Vice President

                                        JANUS INVESTMENT FUND

                                        By: /s/ Girard C. Miller
                                            ------------------------------------
                                            Girard C. Miller, President and
                                            Chief Executive Officer