The acquisition of a conditioned avoidance response (CAR) was investigated in rats of nursing mothers given pimozide 0.5 mg/kg on days 1, 2, 3, 4, 5, 6, and 7 after delivery. Four weeks after birth, the male litter-mates were tested for CAR acquisition in a two-way avoidance situation or for correct CAR acquisition in a brightness discrimination situation. Offspring of mothers treated with pimozide were markedly inferior in the CAR acquisition in both behavioural situations as compared to those of mothers given glucose. The administration of d-amphetamine 15 min prior to the training session specifically counteracted the behavioural impairment obtained in the offspring of pimozide-treated mothers. The results obtained in the present investigation lend further support to the contention that the behavioural deficits in offspring of nursing mothers treated with neuroleptic agents are due to a developmental disturbance in central catecholamine neurones.