We report here the effect of histamine on amylase secretion in isolated lobules from the rat pancreas. Different concentrations of histamine increased amylase secretion, while the stimulatory effect was reduced by cimetidine although not by chlorpheniramine. These findings suggest that pancreatic lobules have H2 receptors. On the other hand, bethanechol induced a stimulatory effect on pancreatic lobules that was inhibited by cimetidine. Vibrio cholerae toxin stimulated amylase secretion, but this effect was not reduced by cimetidine. Cimetidine may thus block the stimulated amylase secretion interfering with the Ca2+ messenger system.