Aims/hypothesis. Interleukin-1 beta (IL-1β) in synergy with tumour necrosis factor alpha (TNFα) and interferon gamma (IFNγ) is cytotoxic to pancreatic beta cells. Mitogen-activated protein kinase (MAPK) activity that is induced by interleukin-1 beta has been suggested to signal nitric oxide-dependent as well as nitric oxide-independent beta-cell destructive pathways. The aim of this study was to investigate if TNFα and IFNγ signal through mitogen-activated protein kinases in isolated rat islets of Langerhans and if they potentiate mitogen-activated protein kinase activity induced by IL-1β.¶Methods. Islets of Langerhans were isolated from 5- to 7-day-old Wistar rats and precultured for 7 days before stimulation with IL-1β, TNFα and/or IFNγ for 20 min followed by lysis. Kinase activity was measured with a whole cell lysate kinase assay and after immunoprecipitation of the kinase using immunocomplex kinase assay.¶Results. Exposure to IL-1β or TNFα significantly increased mitogen-activated protein kinase activity, whereas IFNγ tended to decrease extracellular-signal-regulated kinase activity. Further, TNFα and IFNγ were found to synergistically increase mitogen-activated protein kinase activity induced by IL-1β.¶Conclusion/interpretation. We hypothesise that the synergistic effect of IL-1β, TNFα and IFNγ in the functional inhibition and induction of cell death in pancreatic beta cells is signalled through a synergistic activation of mitogen-activated protein kinase activity [Diabetologia (2000) 43: 1389–1396].