[Janus Letterhead]

January 12, 2010

VIA EDGAR

Mr. Kevin Rupert
Division of Investment Management
U.S. Securities and Exchange Commission
100 F Street, N.E.
Washington, DC 20549-0505

Re: JANUS INVESTMENT FUND (the "Registrant")
    1933 Act File No. 002-34393
    1940 Act File No. 811-1879
    N-SAR - for Period Ended April 30, 2009

Dear Mr. Rupert:

On behalf of the Registrant and its underlying series, Janus Money Market Fund
and Janus Government Money Market Fund (together, the "Funds"), this letter is
to respond to your comment made by telephone on January 5, 2010, and discussed
further on January 7, 2010, with respect to the Registrant's Form N-SAR
Semi-Annual Report filed on June 26, 2009 for the reporting period ended April
30, 2009. The comment of the Staff of the Securities and Exchange Commission
(the "Staff") and the Registrant's response to the Staff's comment is as
follows:

     STAFF COMMENT: The Staff requested that the Registrant review the response
     submitted to Item 74.W regarding the Funds' "mark-to-market net asset value
     per share" or "shadow pricing" value per shares. The Staff noted that the
     Registrant reported a per share value of $1.000 for Janus Money Market Fund
     and requested that the Registrant provide an explanation of the methodology
     used for its shadow pricing calculation. In the event the Registrant
     determines that the value reported was in error, the Staff requested that
     the Registrant re-file the Form N-SAR together with other annual and/or
     semi-annual reports filed on Form N-SAR for the previous four reporting
     periods.

     RESPONSE: The Registrant confirms that the Funds' shadow pricing values per
     share are correct. When responding to Item 74.W of Form N-SAR, the
     Registrant employs a truncation rounding method which the Registrant
     believes is the most conservative rounding approach. The Registrant
     calculates a nine decimal digit mark-to-market net asset value then
     truncates the number (or drops the last five decimal digits) in order to
     determine the required four decimal digit disclosure. Accordingly, on the
     Registrant's April 30, 2009 N-SAR, Janus Money Market Fund's mark-to-market
     net asset value of $1.000092579 was disclosed as $1.0000 for purposes of
     responding to Item 74.W and was not reported in error. If the Registrant
     had employed a



     different rounding method such as "rounding to the nearest value," then
     Janus Money Market Fund's mark-to-market net asset value would have been
     $1.0001.

     Form N-SAR is ambiguous as to the type of rounding method to be used in
     responding to Item 74.W. Given Form N-SAR's ambiguity and the lack of
     materiality resulting from implementing different rounding methods, the
     Registrant believes that the more conservative truncated rounding method is
     more appropriate for the Funds and that a restatement of Janus Money Market
     Fund's mark-to-market net asset value is not needed. However, per the
     Staff's request on January 7, 2010, for future filings, the Registrant will
     use the "rounding to the nearest value" method in calculating its response
     to Item 74.W of Form N-SAR.

The Registrant acknowledges responsibility for the adequacy and accuracy of the
disclosure in the N-SAR filings. In addition, the Registrant acknowledges that
Staff comments, or changes to disclosure in response to Staff comments in the
filings reviewed by the Staff, do not foreclose the Commission from taking any
action with respect to the filing.

If you have any concerns regarding the above responses, please call me at (303)
336-4562. Thank you for your assistance in this matter.

Regards,


/s/ Rodney A. DeWalt

Rodney A. DeWalt
Legal Counsel

cc: Stephanie Grauerholz-Lofton, Esq.
    Jesper Nergaard
    Robin Nesbitt, Esq.