An intraperitoneally located and prevascularized expanded polytetrafluoroethylene solid support is potentially a suitable transplantation site for encapsulated pancreatic islets, because it allows for both the implantation of a large volume islet graft in the immediate vicinity of blood vessels, and its complete removal. The present study investigates the efficacy of such solid supports for the implantation of nonencapsulated islet isografts in streptozotocin diabetic rat recipients. These solid supports were always coated with acidic fibroblast growth factor, because we found that this growth factor enhances the neovascularization. The success rates of 5-microl (group A) and 10-microl (group B) islet isografts in solid supports were compared with the success rates of 5-microl (group C) and 10-microl (group D) islet isografts implanted in the unmodified peritoneal cavity. Four of seven rats in group A and all seven rats in group B became normoglycemic for at least 6 months. Only two of eight rats in group C and four of eleven rats in group D showed normoglycemia. The normoglycemia lasted for at least 6 months in zero of two animals in group C and in three of four animals in group D. Because of the low success rates in groups C and D, intravenous and oral glucose testing were restricted to the successful recipients in groups A and B. Glucose tolerance was found to be proportional to the grafted islet volume but, expectedly, in both groups the glucose tolerance and the insulin responses were somewhat lower than in controls. Thus, the prevascularized expanded polytetrafluoroethylene solid support, rather than the unmodified peritoneal cavity, is an efficacious transplantation site, potentially suitable for encapsulated islets.