Longitudinal studies of plasma dehydroepiandrosterone sulfate (DHEA-S) and dehydroepiandrosterone (DHEA) were made in 13 girls aged 7 years and 14 aged 10 years, during 3 years, at 6-month intervals. Similarly, two groups of 12 boys aged 8 years and 11 years were followed. In addition, 3 girls with premature adrenarche and 4 male patients with Addison’s disease were studied. In the normal girls a significant rise of plasma DHEA-S and DHEA occurred from 6 years of bone age (51.4 ± 9.0 ng/ml and 50.5 ± 9.2 ng/100 ml, respectively) to 8 years (119.7 ± 19.1 ng/ml and 94.5 ± 16.5 ng/100 ml). A further significant rise was apparent at 11 years (385.8 ± 60.9 ng/ml) and 329.0 ± 78.4 ng/ 100 ml). In boys, a similar rise of DHEA-S and DHEA was observed between 6 years of bone age (75.8 ± 12 ng/ml and 44.3 ± 7.6 ng/100 ml) and 8 years (157.4 ± 28.9 ng/ml and 76.1 ± 8.9 ng/100 ml). Further significant rises of DHEA-S and DHEA were seen at 13 years of bone age (563.7 ± 123.7 ng/ml and 267.9 ± 50.0 ng/100 ml, respectively). Testosterone in both sexes rose 2–3 years later than DHEA-S and DHEA. In female patients with premature adrenarche, higher plasma levels of DHEA-S and DHEA were found when compared to normal levels at similar chronological and bone ages. Very low plasma concentrations of DHEA-S and DHEA were observed in the patients with Addison’s disease.