pregnant rats were administered nicotine (0.6 mg/kg/day) during different stages of pregnancy. exposure occurred in either the first trimester (days 1-7), second trimester (days 8-14), third trimester (days 15-21), throughout gestation, or not at all (nonexposed controls). the effects of prenatal nicotine exposure on reproductive, developmental and reflex indices were studied. prenatal nicotine exposure resulted in the birth of smaller sized litters for first trimester exposed dams, as compared to all other groups, except third trimester exposed females. third trimester exposed females gave birth to smaller litters than second trimester and control females. total weights of litters from third trimester females were lower than second trimester and control females. furthermore, developmental age for eye opening was found to be earlier for first trimester animals as compared to third trimester or control rats. also, animals exposed throughout gestation showed eye opening earlier than controls. finally, first trimester exposed animals acquired the righting reflex sooner than all other groups except nonexposed control rats. control animals demonstrated this reflex earlier than second or third trimester exposed rats. prenatal nicotine exposure, in this study, did not appear to influence the acquisition or extinction of behaviorally conditioned immunosuppression in adult rats. the implications of this, regarding nicotine dose, the specific area of the immune system examined, and the developmental age of the subjects, are discussed.