The purpose was to discover whether fluoride (F) accumulates in the pineal gland and thereby affects pineal physiology during early development. The [F] of 11 aged human pineals and corresponding muscle were determined using the F-electrode following HMDS/acid diffusion. The mean [F] of pineal gland was significantly higher (p < 0.001) than muscle: 296 + 257 vs 0.5 + 0.4 mg/kg respectively. Secondly, a controlled longitudinal experimental study was carried out to discover whether F affects the biosynthesis of melatonin, (MT), during pubertal development using the excretion rate of urinary 6-sulphatoxymelatonin, (aMT6s), as the index of pineal MT synthesis. Urine was collected at 3-hourly intervals over 48 hours from two groups of gerbils, (Meriones unguiculatus), low-F (LF) and high-F (HF) (12 f, 12 m/group): under LD: 12 12, from prepubescence to reproductive maturity (at 9-12 weeks) to adulthood, i.e., at 7, 9, 11 1/2 and 16 weeks. The HF pups received 2.3 ug F/g BW/day from birth until 24 days whereafter HF and LF groups received food containing 37 and 7 mg F/kg respectively and distilled water. Urinary aMT6s levels were measured by radioimmunoassay. The HF group excreted significantly less aMT6s than the LF group until the age of sexual maturation. At 11 1/2 weeks, the circadian profile of aMT6s by the HF males was significantly diminished but, by 16 weeks, was equivalent to the LF males. In conclusion, F inhibits pineal MT synthesis in gerbils up until the time of sexual maturation. Finally, F was associated with a significant acceleration of pubertal development in female gerbils using body weights, age of vaginal opening and accelerated development of the ventral gland. At 16 weeks, the mean testes weight of HF males was significantly less (p < 0.002) than that of the LF males. The results suggest that F is associated with low circulating levels of MT and this leads to an accelerated sexual maturation in female gerbils. The results strengthen the hypothesis that the pineal has a role in pubertal development.