Objective: To study basal and ACTH stimulated levels of dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), androstenedione (A4), and cortisol (F) in healthy girls during prepuberty. Patients: Six prepubertal girls, ages 3.7-10.9 years. Study Design and Measurements: The six girls underwent a physical examination and an acute ACTH stimulation test on a yearly basis. Serum DHEA, DHEAS, A4, and F at 0 min (Steroid0) and 60 min (Steroid60) after 0.25 mg ACTH1-24 i.v., and the net increment (ΔSteroid60-0) were calculated. Results: DHEAS0, DHEAS60, DHEA0, DHEA60 and A40 were positively correlated to chronological age. DHEAS0 and DHEAS60 levels rose gradually beginning at 6.1-7.0 years of chronological age, and were found to be significantly different at 9.1-10.0 years and 10.1-11.0 years of age, compared to the median values obtained at ≤6.0 years of age. There was a tendency for DHEA0, DHEA60, and A40 to increase beginning at 9.1-10.0 years of age. Net increment values of all hormones did not change throughout the study. Conclusion: An increase in the circulating level of DHEAS appears to be the first event observed during adrenarche, prior to clinical evidence of the process. © Freund Publishing House Ltd.