Clinical islet transplantation (Tx) in type I diabetic patients has been successful so far only in a minority of cases, probably because of multiple factors, partly immunologic and partly nonimmunologic in nature. Preclinical studies of islet Tx in large animals are still needed to clarify the reasons and find possible solutions. In this study, we tested the feasibility of noninvasive, repeated intrahepatic allo-Tx of porcine pancreatic islets obtained from multiple donors, in pigs rendered diabetic by total pancreatectomy (Pct). In group I Yucatan miniature swine (n = 6), after induction of diabetes by Pct, repeated islet allo-Tx of > or = 80% pure islets was performed. Islets obtained from two pigs of the Hanford breed were injected twice a week, half freshly isolated and half 48-h cultured, over a period of 11 days, for a total of 23,647 +/- 1617 islet equivalents (IE)/kg recipient body weight (BW). In group II Yucatan miniature swine (n = 3), after Pct, a single allo-Tx of > or = 80% pure islets, previously obtained from two donors of the Hanford breed, was performed, using a total of 22,416 +/- 1124 IE/kg BW. In group III Yucatan miniature swine (n = 3), auto-Tx of 60-75% pure islets, averaging 2980 +/- 424 IE/kg BW, was performed a few hours after Pct. Group IV Yucatan mini pigs (n = 3) underwent Pct and were used as diabetic controls. Group V animals (n = 3) were normal control Yucatan mini pigs. Porcine islets were isolated by a modification of the standard collagenase digestion and Ficoll gradient purification method. Donors and recipients were chosen on the basis of moderate to high mutual alloreactivity in mixed lymphocyte culture (MLC). In groups I and II, cyclosporine A (CsA) was started 4 days before allo-Tx, at the dose of 15 mg/kg IM, and then gradually reduced to 4 mg/kg IM. In all group I animals, normal fasting blood glucose (FBG) was restored within 2-3 weeks. Two normoglycemic pigs died of acute pneumonia at 33 and 112 days, respectively, and one animal became progressively hyperglycemic at 100 days. After 3 months, discontinuation of CsA treatment resulted in FBG increase in two group I animals. In one pig, CsA was stopped after 151 days, and normoglycemia persisted until euthanasia, after 8 months. In group II pigs, normoglycemia lasted 4-20 days, with a progressive increase of insulin requirement thereafter. In group III animals, after islet auto-Tx, normoglycemia lasted 7-10 days, while insulin daily requirement progressively increased thereafter, stabilizing at 0.4 IU/kg/day, corresponding to about one third of the amount required in diabetic controls. The single most important result in this series of experiments is that intraportal allo-Tx of a sufficient islet mass, divided in multiple subtherapeutic doses, produced a better metabolic long-term control in comparison to a single injection of the same amount of islets. The technique of multiple-donor repeated islet Tx may prove useful to overcome the problem of primary nonfunction or early graft failure, currently limiting the success of clinical islet Tx in most cases.