Previous studies have shown that prenatal exposure to a moderate dose of ethanol (2 g/kg) during the last days of gestation of the rat (17-20) not only increases postnatal intake of the drug but also enhances the palatability of ethanol's taste when measured with a taste reactivity test. Prenatal administration of the opioid antagonist naloxone, together with ethanol, reduces ethanol intake. The aim of the present study was to analyze whether this decreased intake of ethanol after the administration of naloxone is accompanied by a reduction in ethanol's palatability. Results show that preweanling rats exposed prenatally to ethanol alone displayed more ethanol intake and more ingestive responses in reaction to its taste than non-exposed pups. Simultaneous prenatal administration of naloxone with ethanol prevented both the increased intake of ethanol and the higher amount of appetitive responses to its taste. These results indicate that the opioid system plays an important role in the effect of enhanced palatability of ethanol's taste after its prenatal exposure. Results also support the hypothesis of a conditioned response established in utero as a consequence of the association between ethanol's chemosensory and reinforcing aspects, the latter mediated by the opioid system.