Previous reports indicate an interaction of the adrenals with the pituitary-gonadal axis. In the present study dependence of the time of onset of puberty upon adrenal function was investigated. Vaginal opening and subsequent cyclicity were determined in 4 groups of rats: control, laparotomized, adrenalectomized and adrenal autotransplanted. Since developmental changes in adrenocortical secretion occur prepuberally, surgery was performed at 18, 25 and 35 days of age. The animals remained in good health and were autopsied at 60–65 days of age on either proestrus or estrus; completeness of adrenalectomy and viability of transplants were determined. Ovarian and uterine weights and cycle length were comparable in all groups; all estrous animals had similar ova counts. Laparotomy at any age did not alter the time of vaginal opening (mean = 38 days). Puberty was significantly delayed (p < 0.00005) by adrenalectomy at 18 or 25 days of age, but was not altered by adrenalectomy on day 35. Adrenal autotransplantation at 18 days of age prevented the delay in puberty but was ineffective in the 25-day-old group. The data suggest the existence of a period terminating between 25 and 35 days of age during which adrenal secretions play a role in the maturation of the brain-pituitary ovarian axis. Since adrenal autotransplantation inhibited the adrenalectomy-induced delay in puberty onset, the adrenal stimulatory factor appears to be steroidal rather than a catecholamine. (Endocrinology93: 1232, 1973)