Cytokines have been regarded as effector molecules responsible for beta-cell death and major histocompatibility complex hyperexpression in endocrine pancreas of type I diabetes. However, the mechanism that results in beta-cell-selective destruction has not been elucidated. We demonstrated in this study, using cell lines of transformed mouse beta-cells and alpha-cells, that only pancreatic beta-cells but not alpha-cells produced tumor necrosis factor-alpha when exposed to interleukin-1 beta. Northern blot analysis confirmed the beta-cell-selective expression of tumor necrosis factor-alpha mRNA. Interleukin-1 beta also provoked tumor necrosis factor-alpha mRNA expression in vitro by normal mouse islet cells. Because tumor necrosis factor-alpha has been shown to potentiate beta-cell cytotoxicity of interleukin-1 and interferon-gamma, tumor necrosis factor-alpha produced in situ by beta-cells might be self-destructive. In fact, a low dose of interleukin-1 beta in combination with a low dose of interferon-gamma preferentially injured beta-cells. Hence endogenous tumor necrosis factor-alpha production by beta-cells may be involved in beta-cell-selective destruction in type 1 diabetes.