The effect of antilymphoblast globulin (ALG) as a graft pretreatment for pancreatic islet cell allografts was tested in the canine model. Previous experiences on minimally immunosuppressed renal allografts had demonstrated significant prolongation of survival after graft pretreatment with ALG. ALG was injected with pancreatic islet cell fragment allografts that had been processed by mincing and subsequent collagenase digestion into the splenic pulp after total pancreatectomy of recipients immunosuppressed only with azathioprine following transplantation. Graft survival for pancreatic controls was 5.6 +/- 2.59 (M +/- SD) days. Islet cell allografts that received no ALG had a mean survival of 11.0 +/- 13.99 days (M +/- SD), P greater than 0.1). However, allografts pretreated with ALG had a significantly longer graft survival of 29.6 +/- 18.7 days (M +/- SD,P less than .01). Therefore, the spleen not only is an acceptable site for pancreatic islet cell transplantation in the dog, but significant graft prolongation can be achieved by utilization of ALG as a graft pretreatment modality for recipients receiving minimal immunosuppression with azathioprine.