The long term effects of prenatal protein deprivation were examined in the Albino rat. Females of the Deprived group were placed on an 8% protein diet during gestation only and returned to a normal stock diet after the birth of litters. Offspring were cross-fostered to provide for independent experiences of prenatal and post­ natal conditions. Physical measures from birth to maturity indicated prenatally deprived pups to be permanently retarded in growth. The postnatal environment was considered as an additional source of retardation reflected in the delayed growth of prenatally normal pups fostered to deprived mothers. Emphasis was placed on suitable postnatal controls to determine the relative effects of pre and postnatal variables in deprivational insult. Habituation of the head-shake response to an air-puff stimulus was introduced as a measure of possible long term deprivation effects. Significantly, a long term effect of prenatal deprivation was demonstrated, evident by the greater number of responses required to habituate in prenatally deprived females. This increased responsiveness was seen as a mechanism by which basic learning ability is affected. Habituation as a measure of deprivational insult was found to be an important alternative to previously criticised methods measuring deprivational effects. Extension of its use in this field of research was suggested.