The 24-h mean plasma concentrations of dehydroisoandrosterone (DHA) and dehydroisoandrosterone sulfate (DHAS) and the DHA to DHAS ratio were determined in 37 normal women, aged 21-75 yr, and 32 normal men, aged 21-72 yr. As predicted from our study of sex differences in the metabolism of DHAS, women showed a markely higher DHA to DHAS ratio than men at all ages; the geometric mean for women was 7.5 x 10(-3) and that for men was 3.9 x 10(-3) (P less than 0.0001); and the mean for premenopausal women (6.7 x 10(-3) did not differ significantly from that for postmenopausal women (8.6 x 10(-3)). The two steroids showed a clear-cut linear inverse correlation between concentration and age in both sexes, and menopause was "nonevent" in the age progression for both steroids in the women. The slopes of the concentration vs. age curves were considerably greater in the women, as a reuslt of which the sex differences in concentrations of these steroids changed with age. Under age 50 yr, the plasma DHA concentration of women was considerably higher than that of men [462 +/- 187 (mean +/- SD) vs. 336 +/- 103; P less than 0.025], while the concentrations of DHAS showed no significant sex difference ((77 +/- 38 vs. 101 +/- 67; P greater than 0.1). In persons 50 yr of age or over, plasma DHA concentrations were about the same in women and men (238 +/- 119 vs. 287 +/- 121; P greater than 0.1), but plasma DHAS concentrations were very much lower in women (31 +/- 21 vs. 83 +/- 49; P less than 0.0001).