ethanol-morphine interactions: a study of the effects of prenatal exposure on the development and behavior of the rat. the purpose of the study was to investigate the effects of ethanol, morphine and ethanol-morphine on the physical and behavioral development of the rat. eighteen female and 18 male animals from satinder's heterogeneous stock (shs) were paired. the dams were then exposed to a regimen of either water, or morphine (0.5 mg/ml), or ethanol (10% v/v), or ethanol (10%v/v)-morphine (0.5mg/ml) (high), or ethanol (5% v/v)-morphine (0.25mg/ml) (low), for 21 days during gestation. the 116 surviving offspring were observed daily until weaning (day 28 postpartum) for physical, reflex, and sexual development. following weaning the same offspring were tested for preference towards ethanol and morphine, avoidance learning, reactivity, and hot-plate nociception. there were two instances of delayed physical development one due to ethanol, and one due to ethanol-morphine (high) exposure. there were significant developmental delays due to morphine exposure, and delayed female sexual development due to ethanol, and ethanol-morphine (high) exposure. an overall preference for ethanol was observed regardless of prenatal exposure. this tendency was reversed following morphine, or ethanol-morphine (high) exposure. the consumption of either morphine or ethanol on forced and choice days was dependent on the order of presentation. the postnatal presentation of ethanol and morphine altered food consumption in an order-related pattern. differences due to prenatal exposure were also observed for the one-way avoidance response. it is suggested that the prenatal exposure to ethanol and morphine did not significantly affect learning, while the combination of both agents produced a dose-related hyperresponsivity. the reactivity and the hot-plate testing paradigms were the least sensitive indicators of ethanol-, and/or morphine-induced behavioral effects. the lack of differences is attributed to the limitations of the two testing situations. it is therefore recommended that reactivity testing be extended, and that the hot-plate testing be used in conjunction with postnatal presentation of ethanol or morphine.