We have autotransplanted highly purified cryopreserved canine islets into pancreatectomized dogs. Islets were frozen by slow cooling (0.25 degrees C/min) to -40 degrees C, stored at -196 degrees C and thawed rapidly (200 degrees C/min). A total of 7868 +/- 665 (means +/- SE) cryopreserved islets/kg body weight were implanted to the spleen (n = 7) by venous reflux, and seven other control dogs received 6811 +/- 653 fresh islets/kg (P versus cryo., NS). Fasting plasma glucose [( PG] mg/dl, +/- SEM) and intravenous glucose tolerance were determined before and at 1 and 3 months postimplantation. Six dogs that received cryopreserved islets and all seven control animals promptly became normoglycemic, with PGs of 133 +/- 23 and 110 +/- 4, respectively, at 1 week postimplantation (NS). During follow-up one normoglycemic animal from each group died due to small bowel volvulus and one recipient of fresh islets became diabetic at 14 days. The remaining dogs remained normoglycemic with PGs of 89 +/- 3 and 92 +/- 3 in dogs receiving cryopreserved and fresh islets, respectively, at 3 months postimplantation (NS). Mean K value (decline of glucose, %/min +/- SEM) at ivGTT for all dogs was 2.5 +/- 0.3 preoperatively. At 1 and 3 months postimplantation, the K values of dogs receiving cryopreserved islets were 1.3 +/- 0.1 and 1.4 +/- 0.2, respectively, compared with 1.3 +/- 0.2 and 2.0 +/- 0.2 for control dogs (NS). These data demonstrate prompt and sustained function of a defined quantity of frozen-thawed purified islets in a large mammal. Cryopreservation is an effective method for the long-term storage of purified islet tissue.