The role of leptin as a signal regulating puberty is controversial. Leptin reverses infertility in mice lacking the leptin gene (Nat Gen 1996 137: 3144) and may advance puberty in normal mice (JCI 1997 99: 391). Other reports indicate leptin is only permissive for puberty (Neuroendo 2001 74: 12). Indeed, the pubertal increase in LH is unaffected in juvenile male monkeys given leptin (SFN 2001 #466.9). Since the regulation of puberty differs between male and female primates (J CEM 1995 80: 2094), leptin may affect female puberty despite contrary evidence in males. The present study tested the hypothesis that a nocturnal increase in circulating leptin would advance puberty in female rhesus monkeys. Gonadally-intact females (n = 6) received a daily injection of leptin (30 µg/kg, SC) at 1700 hr from 12 through 24 months of age and were compared to age-matched controls (n = 13). Leptin significantly advanced the onset of secondary sexual characteristics (19.5± .9 vs 21.6± .6 mo, p = .03) and age at menarche (20...