A 42-year-old male began to show frequent hypoglycemic attacks, 25 days after total gastrectomy. By that time, he had received intravenous hyperalimentation therapy with bovine insulin. Incidence of these attacks increased despite the dose of glucose was escalated and insulin administration was interrupted. Serum C-peptide level was 11.4 ng/ml and total immunoreactive insulin (IRI) level was 1170 mu u/ml with 1120 mu u/ml (96%) of gamma-globulin-binding IRI. Since insulin antibody formation was suspected, we decreased the dose of glucose to reduce the endogenous insulin production. Consequently total IRI, binding IRI and C-peptide levels decreased, and hypoglycemic attacks disappeared. These results imply that insulin antibody, once induced by bovine insulin, binds with endogenous insulin. Therefore, it is concluded that heterogenous insulin should not be given during hyperalimentation, especially for patients with good glucose tolerance. When insulin antibody developed, it is effective to reduce the dose of glucose in order to decrease endogenous insulin production.