Ethanol is the leading cause of pancreatitis, but its cellular effects are poorly understood. We examined the direct effects of ethanol, in the concentration range (0.1 - 30 mM) relevant to usual conditions of drinking, on fluid secretion from guinea-pig pancreatic duct cells. Fluid secretion was continuously measured by monitoring the luminal volume of interlobular duct segments isolated from the guinea-pig pancreas. [Ca2+]i was estimated by microfluorometry in duct cells loaded with fura-2. Ethanol (0.3-30 mM) significantly augmented fluid secretion stimulated with physiological (1 pM) or pharmacological (1 nM) concentrations of secretin. It augmented dibutyryl cAMP-stimulated fluid secretion but failed to affect spontaneous or acethylcholine-stimulated secretion. Ethanol (1 mM) shifted the secretin concentration-fluid response curve upward and raised the maximal secretory response significantly by 41%. In secretin-stimulated ducts, 1 mM ethanol induced a transient increase in [Ca2+]i that was dependent on extracellular Ca2+. Ethanol failed to augment secretin-stimulated secretion from ducts pretreated with an intracellular Ca2+-buffer (BAPTA AM) or a protein kinase A inhibitor (H89). In conclusion, low concentrations of ethanol directly augment pancreatic ductal fluid secretion stimulated with physiological and pharmacological concentrations of secretin, which appears to be mediated by the activation of both the intracellular cAMP pathway and Ca2+ mobilization.