Nesidioblastosis, which is the formation of new islets and the differentiation of cells within the islets, represents part of the spectrum of hyperfunctioning states of the islets of Langerhans at the clinical level. Nesidioblastosis in the Syrian golden hamster can be induced by wrapping the head of the pancreas with cellophane tape. Ligation of the duct is not involved, and acinar cell atrophy does not occur. The purpose of this study was to determine whether the induction of nesidioblastosis could be used as a means of reversing streptozocin-induced diabetes. Outbred hamsters (n = 32), 8 wk of age, were rendered diabetic by treatment with 40 mg/kg i.p. streptozocin, administered daily for 3 days. Four days later, 16 animals chosen at random underwent laparotomy with cellophane wrapping of the pancreas. Before surgery, the serum glucose and insulin levels (means +/- SE) in the unoperated control animals (389.0 +/- 18.6, 33.9 +/- 3.8) did not differ from those in the animals awaiting the operation (373.2 +/- 18.6, 37.9 +/- 3.8). After 7 wk, 50% of the operated animals had serum glucose and insulin levels that were normal, compared to only 12% of the unoperated control animals (chi2 = 5.53, P less than .05). Islets from normoglycemic operated animals were characterized by increased numbers, including many small islets, positive immunoreactive insulin staining, and minimal vacuolation of cells. Islets from hyperglycemic operated hamsters and from the unoperated control animals were decreased in number and generally larger in size, demonstrated little or no immunoreactive insulin staining, and exhibited marked vacuolation of cells.(ABSTRACT TRUNCATED AT 250 WORDS)