Seminal fluid concentrations of testosterone (T), dihydrotestosterone (DHT), androstenedione (A), and 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) were measured in 34 male patients of infertile couples. Patients were subdivided into oligospermic (less than 20 X 10(6)/mL) and asthenospermic (typical motility less than 20%; total motility less than 40%) groups. Steroids were measured by specific radioimmunoassay after ether extraction and celite column chromatography. 3 alpha-Diol was present in seminal fluid, and its concentration was significantly correlated with DHT (r = .49, P less than .05). In oligospermic patients, seminal levels of T (78 +/- 29 pg/mL, mean +/- SD) and DHT (323 +/- 132 pg/mL) were significantly reduced in comparison with normospermic men (T, 119 +/- 56, P less than .05; DHT, 557 +/- 255, P less than .01), while A and 3 alpha-diol concentrations were similar in the two groups. Seminal T and DHT levels were also reduced in asthenospermic specimens, which showed increased 3 alpha-diol concentrations (75 +/- 44 pg/mL) with respect to normokinetic samples (45 +/- 20, P less than .05). Finally, a positive linear relationship was observed between DHT and both sperm density (P less than .01) and total motility (P less than .01). These data demonstrate the existence of a significant amount of 3 alpha-diol in seminal plasma and suggest DHT as the androgen most closely related to sperm quality.