In this study, insulin secretion function of INS-1 cells immunoisolated in microcapsules was evaluated. Following encapsulation, the immunoisolated INS-1 cells continued to propagate and flourish within the microcapsules during the entire two-month in vitro incubation period. The insulin secretion from encapsulated INS-1 cells following seven days of in vitro culture increased from 1.6 +/- 0.2 ng/2h/10(6) cells in a glucose-free medium to 11.5 +/- 2.1 ng/2h/10(6) cells at 16.7 mM glucose. In vivo, transplants of 1.2 x 10(7) cells into each of six diabetic C57BL/6 mice resulted in the restoration of normoglycemia in all graft recipients for up to 60 days post transplantation. Most capsules recovered from two animals 30 days post transplantation were free of cell overgrowth and physically intact. Immunostaining for insulin of the cells within the recovered capsules clearly indicated the presence of insulin. The presented data demonstrate the potential use of an immunoisolated beta-cell line for the treatment of diabetes.