Three healthy males (18, 22 and 30 years of age; 85 kg/177 cm, 82 kg/181 cm and 75 kg/168 cm, respectively), synchronized with a diurnal activity (06.00 to 23.00 h) and nocturnal rest, volunteered for this study. Blood was sampled (venous catheter) hourly during a 24 h span. A radiocompetition method was used for cortisol determinations. Other steroids were first extracted (ethyl-ether) from each plasma sample, then chromatographed on a celite column to isolate 3 fractions: 1) Δ4-androstenedione (Δ-4); 2) dihydrotestosterone (DHT) and dehydroepiandrosteone (DHA); 3) testosterone (T). A radioimmunological assay was used thereafter for the determination of androgenic steroids. Statistically significant (both conventional and cosinor methods) circadian rhythms were detected (P < 0.005). Acrophases (peak times) occurred in the following order: cortisol (07.28), DHA (08.43), Δ-4 (09.54), T (11.15) and DHT (16.37). The respective circadian amplitudes of DHA and Δ-4 were smaller than those of cortisol while the amplitudes T and DHT did not show differences statistically significant from each other.