Gas chromatography was used to measure the maternal and fetal plasma inorganic fluoride values at term in 91 women. They were assigned to one of four groups: group A were untreated controls; group B received a single daily dose of 1.5 mg of fluoride (as calcium fluoride) during the final trimester of pregnancy; group C was given a single dose of 1.5 mg of fluoride (as sodium fluoride) and group D was given 2 daily doses of fluoride (as sodium fluoride) totaling 1.5 mg. There was a significant difference between the cord plasma fluoride levels of the newborns in the untreated group (mean: 27.8 micrograms/l) and that of the combined supplemented groups B, C and D (mean: 58.3 micrograms/l). There was no difference between the average fluoride levels in the three supplemented groups. There was no significant effect of maternal age, infant birth weight, gestation or diet during pregnancy on the cord plasma fluoride level. These results indicate that fluoride supplementation during the final trimester of pregnancy will significantly elevate cord plasma fluoride concentrations.