To investigate the role of catecholamine release in emesis, we examined the effects of pretreatment with 6-hydroxydopamine (6-OH-DA) administered into the area postrema in morphine-induced emesis in ferrets. In the 6-OH-DA pre-treated animals, the latency to the first emetic response induced by morphine hydrochloride (1.0 mg/kg, s.c.) was significantly prolonged and the number of retches and emetic episodes was markedly reduced. In the medulla oblongata, the levels of dopamine and homovanilic acid were reduced by 6-OH-DA pretreatment. These results suggest that catecholamine release in the medulla oblongata, mainly dopamine release, may play an important role in morphine-induced emesis in ferrets.