Mullenix et al (Neurotox Teratol 17:169,1995) reported subtle behavioral changes in rats given chronic, high-level exposures to fluoride (F) and suggested that F could cause “IQ deficits and/or learning disabilities in humans.” Objective: To determine the effect of such exposures on learning in rats. Methods: Weanling, female rats (8/group) were given water that provided the following daily doses (mg F/kg) for seven months: Grp 1, 0; Grp 2, 2.9; Grp 3, 5.7; Grp 4, 11.5. The rats, after a 22-h fast, were then trained to press a lever in an operant chamber to receive food pellets. Training was terminated when each rat pressed the lever 75 or more times during a 20-min session for two consecutive days. The rats were then subjected to a fixed ratio (FR) schedule of reinforcement which encouraged high rates of lever pressing. The first day established a ratio of 2-to-1 (FR-2), ie, two presses of the lever were required to receive a food pellet. The ratio was increased each day thereafter: FR-4, FR-6, FR-8, FR-10. For the final ten sessions the rats were placed on a differential reinforcement of low rates of 20 s (DRL-20) which required lower response rates. Specifically, a food pellet was earned only when lever presses followed the previous response by a delay of 20 s or more. Plasma and brain sections were analyzed for F after HMDS-facilitated diffusion. Results: There were no significant differences among the groups in the time required to complete training nor in the FR or DRL-20 schedules. Plasma F concentrations (µmol/L) ranged from 0.3 in Grp 1 to 105 in Grp 4. Brain-to-plasma F concentration ratios were less than 0.30. Conclusion: Graded levels of F exposure had no effect on acquisition of an operant response nor on performance on contrasting high- and low-rate schedules of reinforcement.