LORANCA A., C. TORRERO AND M. SALAS. Development of play behavior in neonatally undernourished rats. PHYSIOL BEHAV 66(1) 3–10, 1999.—The effects of neonatal food and sensory deprivation on play social behavior (boxing, wrestling, and pinning) were studied in male and female Wistar strain rats from 20 to 60 days of age. Data showed that the mean frequency of total play was markedly increased in neonatally underfed subjects. Play did also increase in the females and during the interaction in pairs and in the play that occurred during the prepuberal period. These findings suggest that early food restriction and the unavoidable sensory deprivation associated to the undernourishing procedure, interfere with the neuroendocrine maturational processes of central and peripheral modulatory mechanisms underlying play behavior.