Prazosin was administered orally to 24 normotensive human subjects in the form of capsules or as a solution. Plasma concentrations indicate that drug is almost completely bioavailable from the capsules, although levels peak more slowly than from drug in solution. Drug leaves plasma with a half-life of approximately 2.3 hours. Examination of data from each subject on repeated dosing indicates considerable intrasubject consistency in pharmacokinetic response despite intersubject variability. The absence of the pharmacologically active metabolites in plasma suggests that the hypotensive response derives from drug only. Prazosin is bound to human plasma proteins to the extent of 97%.