The purpose of this study was to determine the F levels in plasma and molar enamel from rat pups whose mothers had received various levels of F during pregnancy and/or lactation. Rats were started on water containing 0 (Group I), 50 (Group II), or 100 (Group III) ppm F at the beginning of pregnancy or on the day of delivery. The mothers and pups were killed 13 days after delivery, and plasma F levels, milk F levels, and pup molar enamel F levels were determined. The mean maternal plasma F concentrations were 0.02 +/- 0.005 ppm in Group I, 0.10 +/- 0.031 ppm in Group II, and 0.21 +/- 0.057 ppm in Group III. The milk F values were about twice as high as the respective plasma concentrations. The plasma F concentration in control pups was 0.003 +/- 0.0002 ppm, and there was a rise to 0.006 +/- 0.0002 ppm in Group III. Enamel F concentrations were 0.62 +/- 0.13 ppm, 4.72 +/- 0.79 ppm, and 8.80 +/- 1.74 ppm, respectively. The plasma and enamel F values obtained from pups were not significantly different between the pre-natal/post-natal, and the post-natal-only groups. It was concluded that: fluoride levels in the plasma and enamel of control rat pups were much lower than those found in adult rats, such values could be increased only slightly when high doses of F were given to the mother, and unlike values reported for other species, rat milk fluoride concentrations were higher than the respective plasma values.