Sexual maturation in female rhesus macaques was studied after surgical isolation of the medial basal hypothalamus [complete hypothalamic disconnection (CHD); n = 4] or after creation of amygdaloid lesions (AMYG; n = 6). In four animals, CHD at 8 months did not affect the age when menarche occurred (30 months) but did result in a significant (P less than 0.01) advancement in age at first ovulation (35.8 +/- 1.1 vs. 43.7 +/- 1.1 months for the five controls). Body weights in CHD and AMYG animals were not different from weights of controls at either menarche or first ovulation, but CHD animals gained weight faster than controls. Although there was no overall difference in age at menarche or first ovulation between AMYG animals and controls, the three AMYG animals that sustained damage to the corticomedial amygdaloid area ovulated later than three other AMYG animals without damage to this area. Daily serum levels of LH, FSH, and 17 beta-estradiol were measured in the second ovulatory cycle of each animal and found to be similar among the three groups. Serum progesterone levels revealed that three of the five controls and one of six AMYG animals had short luteal phases typical of pubertal monkeys, whereas all four CHD animals showed luteal phases typical of sexually mature adult animals. Serum cortisol and PRL showed significant diurnal changes in all three groups. These data indicate that in infant rhesus females, intact neural connections to the medial basal hypothalamus are not obligatory for sexual maturation or for the propagation of entrained diurnal rhythms in cortisol and PRL. That isolation of the medial basal hypothalamus resulted in an increase in the rate of weight gain and favored early sexual maturation may indicate that the main effect of the higher brain centers is inhibitory on hypothalamic mechanisms which control these processes.