BACKGROUND: Islet transplantation is one of regimens supplying the deficient insulin in diabetes patients, but the effects of islet grafts on the changes of endogenous beta-cells are not clear. In the present study, we examined the changes of endogenous beta-cell mass after islet transplantation in partially pancreatectomized mice. METHODS: Balb/c mice were 70% pancreatectomized, transplanted with syngeneic islets (group IV), and were compared with pancreatectomized mice treated with insulin (group III) or no insulin (group II). Blood glucose levels and body weight were monitored. Remnant pancreas was obtained at 6 or 10 days after pancreatectomy, and immunohistochemical staining was done for the evaluation of beta-cell mass changes. RESULTS: Hyperglycemia and weight loss were induced after pancreatectomy. After islet transplantation or insulin treatment, blood glucose levels recovered to normal, and body weight started to increase. Plasma insulin levels were higher and beta-cell mass was larger in group IV than in group II (P < 0.05). Especially, the difference of beta-cell mass between them was more evident at 7 days as compared to at 3 day after transplantation. When compared to group III, group IV showed larger individual beta-cell area after 7 days and larger beta-cell mass after 3 days of islet transplantation (P < 0.05). CONCLUSION: These observations indicate that islet transplantation plays a role in enhancing remnant beta-cell regeneration after partial pancreatectomy in rodents.