This paper reports techniques for the isolation and long term preservation of pancreatic islets from the mouse, rat and guinea pig. Islets have been isolated using a modification of a free hand microdisection procedure described by Hellerström in 1964 [1]. Isolated islets have been subjected to three preservation systems and their viability following storage assessed by light microscopy of sections stained with Gomor's aldehyde fuchsin [2] and by measuring the insulin release from islets in vitro in response to a glucose stimulus. The systems were: a) Simple cold storage in Hank's balanced salt solution at 4 degrees C. Following 15 h cold storage, histological and functional survival was 100%. This dropped to 10% at 48 h. There were no survivors following 72 h storage. b) Sub zero cell storage. In Group I (freezing rate 1 degrees C/min) histological survival was 35% and functional survival 20%. In Group II (freezing rate 5 degreees C/min with 24 h culture period after rewarming) histological survival was approximately 87% and functional survival 75%. c) Organ Culture. Islets from the guinea pig, rat and mouse showed minimal morphologic damage when cultured for 21 days in a simple organ culture system. At 28 days, histological survial was approximately 30%. Following organ culture we were unable to correlate histological and functional survival.