Pregnant female Sprague-Dawley rats were treated from day 12 through day 15 of gestation with procarbazine, an antineoplastic drug, and their offspring were subjected to tests of locomotor development and behavior. Treatment levels ranged from 0.5 mg/kg/day, a dose that produced no abnormalities, to 10 mg/kg/day, a dose that caused a marked micrencephaly in the absence of other teratological changes. Despite marked morphological brain changes, preweaning locomotor development, as assessed by open-field swimming activity and vertical grid climbing, was normal in all offspring. Post-weaning passive avoidance learning and retention were also normal. Groups that had been treated prenatally with teratogenic doses (5.0 and 10.0 mg/kg/day) displayed less rearing behavior in the open field, while ambulation in the periphery of the open field arena was unaffected. Groups treated with subteratogenic doses (0.5 and 1.0 mg/kg/day) did not differ from control. In addition to the behavioral studies, sodium-dependent high-affinity choline uptake and choline acetyltransferase activity (CAT) were measured (per mg protein) in the cortex and hippocampus of animals that had been exposed prenatally to either teratogenic or subteratogenic doses of procarbazine. In spite of a substantial reduction in size of both brain structures in the group receiving a teratogenic dose, choline uptake and CAT did not differ from control.