In order to simulate the elevated corticosteroid and prolactin levels that offspring of stressed mothers may be subjected during breast feeding, rat pups were treated daily with oral corticosterone (200ng/ml milk intake) or prolactin (140ng/ ml milk intake) from the 2nd to the 15th postnatal day. To investigate the potential influence of reduced prolactin intake, the mothers were either treated with bromocriptine (2ug-12ug/rat/day) or 1% ethanol (vehicle). The rat pups were subjected to swim tests from their 8th postnatal day to examine their neuromuscular development. Results from swim tests showed latency in development in the prolactin, corticosterone and prolactin deprived/corticosterone administered groups, compared with the controls. There was decreased daily weight gains in the treatment groups compared to the control. This study demonstrates that increased prolactin and corticosterone and decreased prolactin combined with elevated corticosterone levels to which suckling neonates were exposed to, had a significant negative effect on their neuromuscular adaptive mechanism involved in the normal development of the locomotor system.