OHTSUKA Y., KONDO, T., SHIMADA, M., MURAKAMI, K., IDE, H. and KAWAKAMI, Y. Erythrocyte Insulin Receptor in Insulin Autoimmune Syndrome: Effects of Corticosteroid Therapy. Tohoku J. exp. Med., 1987, 151(2), 181-190 -Changes in the erythrocyte insulin receptors were studied in a patient with insulin autoimmune syndrome before and after corticosteroid therapy. In this case, despite a quite low fasting plasma glucose value (29mg/100ml), a 75g oral glucose tolerance test (OGTT) showed a diabetic curve and extremely high immunoreactive insulin (IRI) levels were observed. After 6 months duration of the disease, corticosteroid was given to the patient and hypoglycemic attacks disappeared with an improvement of the levels of plasma glucose. The number of insulin receptors decreased from 58 to 29 sites/erythrocyte and an increase in binding affinity or maximal binding ability were observed after the treatment with corticosteroid. These receptor changes, for the most part, might be derived from the steroid effects, since there were similar results when we administered steroid for a long term to a certain disease. There was a 20% reduction in the amount of insulin binding IgG purified from the serum one month after treatment with corticosteroid as compared with that purified from the serum before the treatment. The results suggest the usefulness of corticosteroid therapy in treatment of the insulin autoimmune syndrome.