Glucose-induced insulin secretion from islets cultured in the presence of interleukin-6 (IL-6) for 12-24 h was inhibited to a similar extent as when islets were treated with interleukin-1 beta (IL-1 beta). However, unlike IL-1 beta, IL-6 did not potentiate insulin secretion during an acute (30 min) exposure of islets to the cytokine, nor did it inhibit DNA synthesis during a 24 h culture period. A 12 h pretreatment of islets with tumour necrosis factor-alpha (TNF-alpha) combined with IL-1 beta potentiated the inhibitory effect of IL-1 beta on secretion, such that 20 mM-glucose-induced insulin secretion was abolished. No synergistic inhibition of secretion was observed with TNF-alpha and IL-6. However, IL-1 beta and IL-6 were found to inhibit insulin secretion in an additive manner. These results suggest that IL-6 inhibits insulin secretion in a manner distinct from that of IL-1 beta, and that IL-6 is unlikely to mediate the inhibitory effects of IL-1 beta or TNF-alpha on rat islets of Langerhans.