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Several studies have shown that the adult pancreas possesses a limited potential for β-cell regeneration upon tissue injury. One of the difficulties in studying β-cell regeneration has been the lack of a robust, synchronized animal model system that would allow controlled regulation of β-cell loss and subsequent proliferation in adult pancreas. Here we present a transgenic mouse regeneration model in which the c-Myc transcription factor/mutant estrogen receptor ([cMycER.sup.TAM]) fusion protein can be specifically activated in mature β-cells. We have studied these transgenic mice by immunohistochemical and biochemical methods to assess the ablation and posterior regeneration of β-cells. Activation of the [cMycER.sup.TAM] fusion protein results in synchronous and selective β-cell apoptosis followed by the onset of acute diabetes. Inactivation of c-Myc leads to gradual regeneration of insulin-expressing cells and reversal of diabetes. Our results demonstrate that the mature pancreas has the ability to fully recover from almost complete ablation of all existing β-cells. Our results also suggest the regeneration of β-cells is mediated by replication of β-cells rather than neogenesis from pancreatic ducts., The recent success of islet transplantation using purified islets from cadaveric donors presents new opportunities for the treatment of type 1 diabetes (1). However, the severe shortage of donor pancreata [...]