Female rats were given single intraperitoneal doses of fluoride (F) (0, 4, 7, or 14 mg F/kg body weight). Plasma F levels returned to predose values within 24 h. Incisors from animals killed 35 or 70 days after the F doses had been given were analyzed for mineralization defects by microradiography, and for F and P concentrations by nuclear microprobe. At 35 days, all F-injected rats had enamel fluorosis. At 70 days, by which time the incisors would have been renewed nearly twice, fluorosis was still evident in the 14 mg/kg body weight group. The enamel and dentin F concentrations at each time point were proportional to the administered F doses that had been given weeks earlier. The F concentrations at 35 days were similar to those found at 70 days. The results support the hypothesis that, following pulse loading, F can be mobilized from the bone adjacent to the enamel organ and result in local F concentrations sufficiently large to adversely affect amelogenesis.