We found no significant difference between the means for ionic, bound, and total fluoride concentrations in the plasma of male and female subjects of the same age, living in a community with fluoridated water. When results for the 264 fasting subjects were therefore combined according to age, they indicated that persons over 60 years of age have a significantly higher mean ionic (3.89 mumol/L) and total (6.58 mumol/L) fluoride concentration in plasma than do younger age groups. For younger age groups, means ranged from 2.74 to 3.05 mumol/L for ionic fluoride and from 4.74 to 5.58 mumol/L for total. The bound fluoride concentration was lower in individuals 21 to 30 years of age (1.89 mumol/L) than in older age groups (for whom means ranged from 2.42 to 2.68 mumol/L), but was not significantly different from that of individuals who were younger (2.21 mumol/L). A tendency for the mean ionic fluoride concentration to increase with age was noted, but the concentration was significantly higher than the preceding decade group only in those persons over 60 years of age.