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Exhibit 21

SUBSIDIARIES OF THE REGISTRANT

Lung Rx, Inc., a Delaware Corporation
Unither Telmed, Ltd, a Delaware Corporation
Unither Pharmaceuticals, Inc., a Delaware Corporation
United Therapeutics Europe, Ltd., a United Kingdom Company
Unither Therapeutik, GmbH, a German Company
Unither Pharma, Inc., a Delaware Corporation
Medicomp, Inc., a Delaware Corporation
Unither Neurosciences, Inc., a Delaware Corporation
Unither.com, Inc., a Delaware Corporation
LungRx Limited, a United Kingdom Company
Unither Biotech Inc., a Canadian Company
Unither Virology, LLC, a Delaware Corporation

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Exhibit 21

SUBSIDIARIES OF THE REGISTRANT