The 24 h integrated concentrations of progesterone, 17-hydroxyprogesterone (17-OHP) and cortisol were determined in 5 male subjects ranging in age from 25 to 36 years. Using a nonthrombogenic catheter and a constant withdrawal pump, blood was collected for a period of 24 h in 30 min aliquots. All five subjects had similar 24 h integrated concentrations of cortisol (9.2 +/- 5.4). One subject had elevated 24 h integrated concentrations of progesterone (55.2 +/- 18.7) and 17-OHP (352 +/- 122) when compared to the mean integrated concentrations (progesterone: 24.9 +/- 4.7; 17-OHP: 109 +/- 33) of the 4 other subjects. The 30 min integrated concentrations showed a diurnal variation for both 17-OHP and cortisol but not for progesterone. The best correlation between cortisol and 17-OHP occurred when the concentration of 17-OHP 90 or 120 min earlier. No significant correlation occurred between cortisol and progesterone.