Refined methods of islet cell purification have led to unprecedented success of islet cell allotransplantation via portal vein infusion in diabetic patients, resulting in marked reduction of exogenous insulin requirements and recently even insulin independence. The authors report the histologic findings of islet cell allografts in the liver of four patients who had undergone combined kidney-islet or liver-islet transplantation. Islet cell clusters were detected in subcapsular location at the edge of portal triads. The early post-transplant period was characterized by patchy mixed portal infiltrates. Only minimal inflammation but decreased islet cell granulation was observed in one patient 6 months after transplantation. As histologic detection of transplanted islet cells becomes available, additional parameters for evaluation of graft survival might be defined by morphologic assessment.