The effect of peripherally administered drugs that modify monoaminergic function, on ethanol (2.0 g kg-1, intragastrically)-induced changes in urine output has been examined in rats. The alpha-noradrenoceptor agonist, clonidine (0.05-0.15 mg kg-1) produced marked urine output and potentiated slightly the diuretic effect of ethanol. The alpha-noradrenoceptor antagonist, phentolamine (1-5 mg kg-1) dose-dependently decreased ethanol-induced diuresis. p-Chloroamphetamine (0.8-2.0 mg kg-1) produced significant diuresis and potentiated the diuresis produced by ethanol. Methysergide (1.25, 2.5 mg kg-1), a 5-hydroxytryptamine receptor antagonist, had no effect on urine output while it depressed the ethanol-induced increase in urine output. Apomorphine (0.8, 1.5 mg kg-1), a dopamine receptor agonist, did not modify urine output in either control or ethanol-treated animals, while the dopamine receptor antagonist, pimozide (0.75-3.0 mg kg-1), dose-dependently decreased ethanol-induced diuresis, but had no effect on urine output in control animals. Since our previous research indicates that the intraventricular administration of drugs that alter dopaminergic and 5-HT function does not alter ethanol-induced diuresis, the interaction of these types of agents with ethanol-induced diuresis in the present study suggests that the interaction was mediated peripherally.