Ethanol strongly augments secretin-stimulated, but not acetylcholine (ACh)-stimulated, fluid secretion from pancreatic duct cells. In order to understand its mechanism, we examined the effect of short-chain n-alcohols on fluid secretion and intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in guinea pig pancreatic ducts. Fluid secretion was measured by monitoring the luminal volume of isolated interlobular ducts. [Ca²⁺]_i was estimated by fura-2 microfluorometry. Methanol and ethanol at 0.3-10 mM significantly augmented fluid secretion and induced a transient elevation of [Ca²⁺]_i in secretin- or dibutyryl cAMP-stimulated ducts. However, they failed to affect fluid secretion and [Ca²⁺]_i in unstimulated and ACh-stimulated ducts. In contrast, propanol and butanol at 0.3-10 mM significantly reduced fluid secretion and decreased [Ca²⁺]_i in unstimulated and stimulated ducts with secretin, dbcAMP or ACh. Both stimulatory and inhibitory effects of n-alcohols completely disappeared after their removal from the perfusate. Propanol and butanol inhibited the plateau phase, but not the initial peak, of [Ca²⁺]_i response to ACh, as well as the [Ca²⁺]_i elevation induced by thapsigargin, suggesting that they inhibit Ca²⁺ influx. Removal of extracellular Ca²⁺ reduced [Ca²⁺]_i in duct cells and completely abolished secretin-stimulated fluid secretion. In conclusion, there is a distinct cut-off point between ethanol (C2) and propanol (C3) in their effects on fluid secretion and [Ca²⁺]_i in duct cells. Short-chain n-alcohols appear to affect pancreatic ductal fluid secretion by activating or inhibiting the plasma membrane Ca²⁺ channel.