1. Intra-arterial injection or infusion of prostaglandins E(1) and E(2) into anaesthetized cats caused a fall in arterial blood pressure, a reduction in pancreatic blood flow and an inhibition of secretin-stimulated pancreatic electrolyte secretion. In some experiments these effects were preceded by a transient increase in blood flow and secretion.2. The fall in blood pressure and reduction in blood flow, but not the inhibition of secretion, were much less marked following administration of the alpha-adrenergic blocking agent phenoxybenzamine.3. Prostaglandins F(1alpha) and F(2alpha) caused only a slight reduction in blood pressure and had very little effect on pancreatic blood flow or electrolyte secretion.4. Addition of prostaglandins to the perfusate of the saline-perfused cat pancreas stimulated electrolyte secretion, with E(1) = E(2) >> F(1alpha) = F(2alpha). This stimulatory action was markedly potentiated by theophylline.5. Enzyme secretion was not stimulated by any of the prostaglandins, even in the presence of theophylline.6. It is concluded that prostaglandins can stimulate electrolyte transport by exocrine pancreas, perhaps through a mechanism involving adenylate cyclase, but that in vivo this action is masked by a secondary inhibition resulting either from vasoconstriction, or from the libration of an antisecretory agent, or both.