The objective of the current investigation was to describe the pharmacokinetics and absolute oral bioavailability of epristeride. Twelve healthy male subjects (mean (SD) age, 27 (6.2) years) received a single oral dose of 5mg and an intravenous infusion of 4.5 mg over 30 min in a crossover fashion. Blood samples were obtained over 72 h for the determination of epristeride plasma concentrations using a sensitive high-performance liquid chromatography assay. The lower limit of quantification was 5ngmL-I. Pharmacokinetic analysis of the plasma concentration-time data was performed by both noncompartmental and compartmental methods. Absolute bioavailability was determined using dose-normalized AUC values following oral and intravenous administration. Epristeride plasma concentrations declined in a biexponential fashion with secondary peaks evident around 24 h in a majority of subjects following both routes of administration. Maximal plasma concentrations were typically achieved approximately 4 h after oral dosing. The mean apparent terminal elimination half-life estimates were similar following intravenous and oral administration and were 27.3 and 26.2 h, respectively. The mean plasma clearance and steady-state volume of distribution were 0.33 (0.09) rnLmin-'kg-' and 054 (0.17)Lkg-l, respectively. The mean absolute bioavailability was 93% (95% C I 84%, 104%). Following compartmental analysis of the intravenous data, the mean (SD) 1 1 and 12 half-life estimates were 2.74 (0.48) and 31.8 (19.5)h, respectively. The % AUC associated with the 12 exponential phase was approximately 68%. This long half-life allows for once-daily dosing of epristeride.