||To evaluate the effects of styrene exposure on learning, adult male Long-Evans rats learned repeated reversals of a spatial discrimination task. Styrene monomer was administered by gavage to groups of eight rats at 500 mg/kg/day, 5 days/week, for 8 weeks in Experiments (Exps) I and II (total dose = 20.0 g/kg) or for 1, 3, 5, or 8 weeks in Exp III (total dose = 2.5, 7.5, 12.5, or 20.0 g/kg). Control rats received corn oil vehicle for 8 weeks. Reversal training began 8 (Exp I), 10 (Exp II), or 32 (Exp III) weeks after termination of dosing. Serial reversal learning was quantified in terms of trials to criterion. Reversal learning improved similarly in control and treated rats trained under an instrumental (IN) schedule, whereas treated rats trained under an automaintenance (AU) schedule failed to improve as much as controls. Reversal learning of some styrene-treated AU rats in Exp III continued to be impaired for > 1 year after treatment. Not all treated rats were affected by styrene; nevertheless, changes in the affected individuals were as large as those previously observed after trimethyltin-induced lesions of the CNS. The incidence of impairment was not related to the total dose of styrene given, suggesting the action of other, undetermined factors affecting individual sensitivity to styrene.