The objective of this study was to evaluate the absolute bioavailability and acute pharmacokinetics of treprostinil sodium administered by continuous, short-term subcutaneous infusion in normal subjects. Fifteen healthy volunteers received treprostinil via an intravenous infusion at 15 ng/kg/min over 150 minutes, followed by a 5- to 7-day washout and a subcutaneous infusion at the same rate administered over 150 minutes. Serial plasma samples were collected predosing, during dosing, and postdosing, and plasma treprostinil concentration levels were measured by a validated liquid chromatography atmospheric pressure ionization tandem mass spectrometry (LC/MS/MS) method with a lower limit of quantitation (LLOQ) of 25 pg/mL. Acute administration of treprostinil administered by subcutaneous infusion at a rate of 15 ng/kg/min for 150 minutes achieved a mean Cmax of 1.47 ng/mL. Mean AUC infinity values for intravenous and subcutaneous dosing were 3.52 and 3.97 ng.h/mL, respectively, resulting in a mean apparent absolute bioavailability of 113% for subcutaneous administration. It was possible that the area under of the curve for the intravenous administration was underestimated because most of the terminal elimination phase could not be documented due to the LLOQ of the assay. The mean apparent elimination half-life of treprostinil following subcutaneous administration was 1.38 hours, compared to 0.87 hours following intravenous administration. It was concluded that treprostinil administered by subcutaneous administration is completely absorbed, with a slightly longer half-life compared to intravenously administered treprostinil.