Total or near total pancreatectomy is the surest way to relieve the pain of chronic pancreatitis but rarely applied because the metabolic consequences are so severe. For most patients drainage procedures are applicable, but pancreatectomy may be the only alternative for small duct disease or where procedures to improve duct drainage have failed. Preservation of endocrine function is a major problem in patients who require pancreatectomy. Experiments in pancreatectomized dogs have shown that intrasplenic or intraportal transplantation of unpurified pancreatic islet tissue dispersed by collagenase digestion can prevent diabetes. We have applied this technique to ten patients with chronic pancreatitis, small ducts, and intractable pain. The entire pancreas or >95% of the pancreas was excised, minced, dispersed by collagenase digestion and infused into the portal vein <2 1/2 hours after removal. Mean (±SD) rise in portal pressure was 17 ± 8 cm of water. Liver function tests were altered minimally. All patients were relieved of pain. One patient died of a complication not related to the islet autotransplant; viable islets were identified in the liver at autopsy. Of the remaining nine patients, three have been insulin independent for 1, 9, and 38 months. One patient was insulin independent for 15 months and now takes 12 units of insulin daily. Three have nonketosis prone diabetes (tested by insulin withdrawal) and take 15-30 units of insulin per day. C-peptide studies in these patients show that functioning islets are present. Two patients are diabetic and require 35 and 60 units of insulin per day. In eight of nine patients tested serum insulin concentrations fell to undetectable levels during the interval between pancreatectomy and islet transplantation. Serum insulin levels during the first few hours after islet transplantation predicted success. In the insulin independent or in the patients with mild diabetes, insulin levels were persistently ≥6 μU/ml. In the other two patients, the increase in insulin concentration was not sustained. Islet tissue preparation from a diseased pancreas is difficult. The surgeon and the patient must still be willing to accept diabetes for relief of pain when performing this operation. In some patients, however, islet autotransplantation can prevent or partially ameliorate diabetes after pancreatectomy, and preservation of endocrine function is worthwhile.