Monolayer cultures of neonatal rat pancreatic cells were examined to ascertain whether they synthesize prostaglandin E (PGE) and to determine the effects on insulin secretion caused by PGE and drugs that inhibit its synthesis. PGE release into the medium was observed. Sodium salicylate and ibuprofen (at drug concentrations similar to those achieved therapeutically in humans in vivo) inhibited PGE synthesis in a dose-responsive fashion to a maximum of 70-80% inhibition. Inhibition of PGE synthesis was accompanied by augmented insulin secretion. Both PGE synthesis inhibitors shifted the glucose dose-insulin response curves to the left at low glucose concentrations and augmented maximal insulin release at high glucose concentrations. Increments in glucose-induced insulin secretion induced by sodium salicylate correlated well (r = 0.89) with inhibition of PGE synthesis and addition of exogenous PGE1 to the cultures reversed the augmenting effects of the drug on insulin secretion. It is concluded that cultures of pancreatic cells synthesize PGE and that a function of PGE in these cultures appears to be a tonic negative modulation of glucose-induced insulin secretion.