Exhibit 10.5

AMENDMENT

     THIS AMENDMENT is made as of the 21st day of December, 2000 to the
Executive Employment Agreement (the “Agreement”) between Martine Rothblatt
(“Executive”) and United Therapeutics Corporation (“UT”) dated April 2, 1999.

     WHEREAS, the Board of Directors of UT unanimously approved an amendment to
the Agreement at its December 14, 2000 board meeting;

     NOW THEREFORE, the parties hereby amend the Agreement as follows:

     1.     Section 3.2(a) of the Agreement shall be replaced in its entirety by
the following new Section 3.2(a):

                       “Annual Incentive Compensation. During each year of the
term of this Agreement, options to purchase such number of shares, exercisable
for ten years at 110% of the fair market price at the time of grant, as is equal
to, for the first year, the quotient of one percent of the difference in UT
market capitalization from the date of IPO to the one year anniversary thereof
divided by $18.00. For each year thereafter, commencing with the period
beginning December, 2000 and with the next option grant to be made on January 2,
2002, an option to purchase such number of shares, valid for ten years and
exercisable at 110% of the fair market price at the time of grant, as is the
quotient of one percent of the rise in market capitalization of UT from December
2000 to December 2001 calculated using the average Nasdaq closing price during
the month of December of each year, divided by $18.00. Incentive compensation
shall be vested when earned. The maximum incentive compensation that may be
earned shall be capped by the projected market capitalization of UT at the end
of each year under the January 1999 UT Business Plan.”

     In witness whereof, the parties have executed this Amendment effective as
of the date first written above.

      MARTINE ROTHBLATT   UNITED THERAPEUTICS CORPORATION

 

/s/ Martine Rothblatt   /s/ Fred Hadeed

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    Fred Hadeed, CFO