Progesterone can be detected in male plasma and has been considered to originate mainly from the adrenals. We have examined the association between circulating progesterone and obesity in a sample of thirty-eight lean to morbidly obese men aged 44.5 +/- 9.9 years (BMI: 44.3 +/- 12.8 kg/m (2)). Plasma concentrations of progesterone, 17-OH-progesterone as well as androstenedione, testosterone, DHT and DHEA-S were determined. Negative correlations were observed between plasma progesterone levels and body weight (r = - 0.47, p < 0.05), BMI (r = - 0.56, p < 0.001), waist circumference (r = - 0.58, p < 0.001), as well as subcutaneous adipocyte diameter (r = - 0.50, p < 0.05). Plasma levels of 17-OH-progesterone, DHEA-S, androstenedione, testosterone and DHT were also negatively associated with body weight, BMI and waist circumference. However, the ratio of 17-OH-progesterone-to-progesterone and androstenedione-to-17-OH-progesterone were not related to these variables. A positive correlation was found between circulating progesterone and DHEA-S levels (r = 0.50, p < 0.002 after adjustment for age). Accordingly, using multivariate regression analyses, the best steroid predictor of progesterone level was plasma DHEA-S. Waist circumference was the best predictor of progesterone levels in a multivariate model including steroid concentrations as well as waist circumference, BMI and subcutaneous adipocyte diameter. In conclusion, plasma progesterone was negatively associated with markers of obesity such as BMI, waist circumference and subcutaneous adipocyte diameter in this sample of men. Circulating DHEA-S level was the best steroid correlate of plasma progesterone. We suggest that the low progesterone levels observed in obese men may reflect decreased adrenal C(19) steroid production in the adrenal cortex. Further research is needed to confirm this hypothesis.