Changes in plasma and nail fluoride concentrations in rats given different concentrations of fluoride in drinking water were investigated. Six groups of weanling male Wistar rats were provided drinking water containing NaF at 0, 7, 14, 28, 56, or 100 ppm F- for 42 days. The nails were clipped on days 21, 28, 35, and 42; plasma was collected on day 42. The nails and plasma were analyzed with a fluoride ion electrode following HMDS-facilitated diffu- sion. At the end of the study, a direct relationship was evident between the nail and plasma fluoride concentrations (r = 0.67, p < 0.001), indicating that nails can be used as indicators of plasma fluoride concentrations during chronic fluoride intake in rats.