To assess sleep-associated changes in gonadotropin-releasing hormone secretion during sexual maturation, we studied nighttime and daytime patterns of LH and FSH secretion in two groups with qualitatively similar sex steroid levels: girls with central precocious puberty and young adult women in the early follicular phase of an ovulatory menstrual cycle. In the girls with central precocious puberty, all indices of LH secretion were significantly higher at night than during the day (mean LH levels, 12 ± 2 versus 5 ± 1 IU/L, p < 0.01; LH pulse amplitude 16 ± 2 versus 7 ± 1 IU/L, p < 0.01; and LH pulse frequency 0.70 ± 0.05 versus 0.35 ± 0.08 pulse/patient-h, p < 0.01). Girls with a history of menses, who were presumably the most mature, lacked this diurnal variability. Mean nocturnal FSH levels were only slightly higher than daytime levels (7.6 ± 0.5 versus 7.2 ± 0.5 IU/L, p < 0.05) resulting in alternating periods of LH (nighttime) and FSH (daytime) predominance in this pubertal population. In contrast, the adult women had lower mean gonadotropin levels and LH pulse frequencies at night than during the day (mean LH 7 ± 1 versus 10 + 1 IU/L, p < 0.05; mean FSH 9 ± 1 versus 10 ± 1 IU/L, p < 0.05; LH pulse frequency 0.40 ± 0.08 versus 0.70 ± 0.10 pulse/patient-h, p < 0.05) and often (six of eight) demonstrated striking suspension of gonadotropin-releasing hormone secretion during sleep. The smaller changes in FSH again resulted in periods of relative LH (daytime) and FSH (nighttime) predominance. When between-group comparisons were made, the girls with central precocious puberty differed significantly from the women in the early follicular phase with respect to each index of gonadotropin secretion except for daytime LH pulse amplitude. Thus, neuroendocrine maturation in the human female appears to be characterized by changes in both the pattern of gonadotropin-releasing hormone secretion and the daily alternating periods of relative LH and FSH predominance in response to sleep.