PROMISSORY NOTE

Exhibit 10.1

PROMISSORY NOTE

For Value Received , MannKind Corporation , a Delaware corporation (“ Borrower ”), hereby promises to pay to the order of The Mann Group LLC (“ Lender ”), in lawful money of the United States of America and in immediately available funds, the principal sum of up to Three Hundred and Fifty Million Dollars ($350,000,000) or the aggregate principal amount of all Advances (as defined below) made hereunder, whichever is less (the “ Loan ”) together with accrued and unpaid interest thereon, each due and payable on the dates and in the manner set forth below.

      1. Principal Repayment. The outstanding principal amount of each Advance together with all accrued and unpaid interest thereon shall be due and payable on December 31, 2011 (the “ Maturity Date ”).

      2. Interest Rate. Borrower further promises to pay interest on the outstanding principal amount of each Advance from the date thereof until payment in full, which interest shall be payable at a rate equal to the one year London Interbank Offered Rate (LIBOR) reported by the Wall Street Journal (or a comparable periodical if such periodical is no longer published) on the day of such Advance plus 3% per annum, or the maximum rate permissible by law (which under the laws of the State of California shall be deemed to be the laws relating to permissible rates of interest on commercial loans), whichever is less. Interest shall be due and payable quarterly in arrears not later than the first day of each calendar quarter for the preceding quarter, commencing on the first day of the calendar quarter following the calendar quarter in which an Advance is made, and shall be calculated on the basis of a 365/366-day year for the actual number of days elapsed.

      3. Place of Payment. All amounts payable hereunder shall be payable in lawful money of the United States of America at the office of Lender, 28903 North Avenue Paine, Valencia, CA 91355, unless another place of payment shall be specified in writing by Lender.

      4. Application of Payments; Prepayment.

           4.1 Payment on this Note shall be applied first to accrued interest, and thereafter to the outstanding principal balance hereof.

           4.2 This Note may be prepaid in whole or in part without penalty or premium. Any amount prepaid pursuant to this Section 4.2 may be reborrowed subject to Section 5 hereof. Any partial prepayment made pursuant to this Section 4.2 shall be applied to interest first and then to principal, and shall be applied to the oldest outstanding Advance first. At the time of any prepayment of principal hereunder, Borrower shall also pay all accrued and unpaid interest on the amount prepaid through the date of prepayment.

           4.3 At any time after January 1, 2010, upon delivery of prior written notice (the “ Call Notice ”), Lender may require Borrower to prepay Advances that have been outstanding for more than twelve months as of the date of the notice. Lender may

not require Borrower to prepay Advances in an aggregate amount exceeding $200,000,000 pursuant to this Section 4.3. If Lender exercises such call right, Borrower shall, on the earlier of: (x) 180 days after delivery of the Call Notice or (y) the Maturity Date, prepay the Advances in the amount set forth in the Call Notice. Any partial prepayment made pursuant to this Section 4.3 shall be applied to interest first and then to principal. At the time of any prepayment of principal hereunder, Borrower shall also pay all accrued and unpaid interest on the amount prepaid through the date of prepayment.

      5. Loan Requests. Provided that no Event of Default has occurred and is continuing, from and after the date hereof and through and including December 31, 2011, Lender shall make available to Borrower for borrowings by Borrower from time to time a principal amount of Three Hundred and Fifty Million Dollars ($350,000,000) less the aggregate principal amount of the Advances outstanding on the date hereof (each, an “ Advance ”). Whenever Borrower desires an Advance hereunder, Borrower shall notify Lender by facsimile with a transmission confirmation or by electronic mail as long as a read receipt is requested and received no later than 4:00 p.m. Pacific time, sixty (60) calendar days prior to the date on which the Advance is requested to be made. At the time of any Advance (or at the time of receipt of any payment of principal), Lender shall make or cause to be made, an appropriate notation on the Exhibit A attached hereto reflecting the amount of such Advance (or the amount of such payment). The outstanding amount of this Note set forth on such Exhibit A shall be prima facie evidence of the principal amount thereof outstanding, but the failure to record, or any error in so recording, shall not limit or otherwise affect the obligations of Borrower to make payments of principal of or interest on this Note when due.

      6. Representations and Warranties. The Borrower hereby represents and warrants to the Lender as follows:

           6.1 The Borrower has the requisite power and authority to enter into this Note and to consummate the transactions contemplated hereby. The execution and delivery of this Note by the Borrower and the consummation by the Borrower of the transactions contemplated hereby have been duly authorized by all necessary corporate action on the part of the Borrower. This Note has been duly executed and delivered by the Borrower and constitutes the legal, valid and binding agreement of the Borrower enforceable against the Borrower in accordance with its terms, except as may be limited by (i) applicable bankruptcy, insolvency, reorganization, moratorium and other laws of general application affecting enforcement of creditors’ rights generally and (ii) equitable principles of general applicability relating to the availability of specific performance, injunctive relief or other equitable remedies.

           6.2 No consent, approval, authorization, order, license, registration or qualification of or with any Governmental Entity is required for the execution and delivery by the Borrower of this Note or the transactions contemplated hereby, except such consents, approvals, authorizations, orders, licenses, registrations or qualifications as have been obtained, or which, if not obtained, would not, individually or in the aggregate, have a material adverse effect on the ability of the Borrower to perform its obligations hereunder or consummate the transactions contemplated hereby on a timely basis.