Isolated islets from adult rats or obese hyperglycemic (ob/ob) mice were incubated with human recombinant interleukin 1β in order to study whether the acute effects of the cytokine on islet insulin release are associated with changes in islet phospholipase C activity, Ca²⁺ handling or protein phosphorylation. The cytokine stimulated insulin release both at low and high glucose concentrations during one hour incubations. In shortterm incubations (<1 min) interleukin 1β did not affect the production of inositoltrisphosphate. Addition of interleukin 1β affected neither the cytoplasmic free Ca²⁺ concentration at rest nor that observed subsequent to stimulation with a high concentration of glucose. Furthermore, the endogenous protein kinase C activity, as visualized by immunoprecipitation of a ³²P-labelled substrate for this enzyme, was not altered by interleukin 1β. Separation of ³²P-labelled proteins by means of 2-dimensional gel electrophoresis failed to reveal any specific effects of the cytokine on the total protein phosphorylation activity. These results suggest that the stimulatory effects on insulin release exerted by interleukin 1β are not caused by acute activation of phospholipase C and protein kinase C or by an alteration of islet Ca²⁺ handling of the B-cells.