The concentrations of the antiandrogenic endogenous steroid epitestosterone (epiT) and of testosterone, dihydrotestosterone (DHT) and androstenedione in the prostate were determined in tissue samples obtained from 21 patients who underwent suprapubic prostatectomy for benign prostatic hyperplasia. Fifteen patients received no hormonal treatment before surgery and the other 6 patients were pretreated for 8 weeks before surgery with an oral dose of 5 mg/day finasteride. The steroids were extracted and separated by high pressure liquid chromatography and determined by specific radioimmunoassays. The concentration of epiT (mean 58.4 +/- 40.4 S.D., range 14.0-144.0 fmol/mg protein) exceeded that of testosterone and was nearly as high as that of DHT. The prostatic tissue from the patients treated with finasteride for 8 weeks showed a significant decrease not only in DHT but also in androstenedione and epiT, whereas the concentration of testosterone increased significantly.