Remission of diabetes, i.e. significant amelioration from absolute insulin-dependency, has been sometimes observed in diabetic BB/Wor//Tky rats which were treated with insulin. In remission BB/Wor//Tky rats, plasma glucose levels improved to near normal level and insulin content was also preserved as much as that between diabetic and non-diabetic rats. In this process, we hypothesized that autoimmune insulitis was suppressed and remaining islet B-cells was restored from severe destruction by recovering in number and/or function. While, recently, a novel regenerating (reg) gene, identified in the regenerating pancreatic islets of surgical models, is reported to be related to the replication of pancreatic B-cells in vitro. Based on these findings, we histologically investigated whether the reg protein could be actually expressed or not in the islets from remission BB/Wor//Tky rats. As expected, reg protein was observed in the islets from remission BB/Wor//Tky rats mainly in accordance with pancreatic B-cells. Thus, the present findings suggested that the regeneration of pancreatic B-cells represented by the expression of reg protein might be, at least in part, relevant to remission induced by insulin therapy in spontaneously occurring Type 1 diabetes in BB/Wor//Tky rats.