Male and female Fischer 344 rat pups were exposed to either DMSO or chlordecone (Kepone) by s.c. injection on day 4 postnatally. Chlordecone had transient effects on body weights and resulted in precocial vaginal opening (vaginas open at day 21 of age). At approximately 100 days of age, one half of the animals were trained on a variable interval (VI) 15 sec schedule of food reinforcement. Rates of free operant activity differed during training of the VI and chlordecone-treated females had lower baselines than controls following establishment of baseline responding. Baselines of males were not affected. Chlordecone-exposed rats were affected the same as controls by d-amphetamine (0.25-2 mg/kg) and apomorphine (0.025-0.1 mg/kg). The remaining rats were trained to make a visually cued nose poke response for food in a discrete trial discrimination task. Few differences were noted during acquisition of the task over a three week period. However, marked alterations in responding were observed during two weeks of reversal. These data indicate that a single postnatal injection of chlordecone can produce subtle, long-lasting neurobehavioral changes in rats. The nature of these changes appear to be alterations in their reactivity to novel or changing conditions.