The circadian profiles of cortisol and dehydroepiandrosterone sulphate (DHEA-S) were analyzed in a homogeneous group of 15 young normally cycling women, at 4 times of the menstrual cycle: early follicular (EF), late follicular (LF), early luteal (EL) and late luteal (LL) stages. The circatrigintan variations of the same hormones were also evaluated. Population-mean cosinor analysis allowed the demonstration of a highly significant circadian periodicity for both variables in any of the 4 stages of the menstrual cycle; on the other hand, the same computation failed to demonstrate a significant circatrigintan periodicity. In each of the stages considered, the circadian acrophase of DHEA-S was delayed in comparison to that of cortisol, being located in the early afternoon hours. The demonstration of a clear-cut circadian oscillation in serum DHEA-S prompts studies on possible chrono-abnormalities of the steroid production in women with hyperandrogenic diseases.