Male rats of approximately 200 gm. body weight were injected intravenously with alloxan (40 mg. per kilogram body weight). Blood glucose determinations were carried out at periodic intervals. Plasma samples and acid alcohol extracts of pancreas were assayed by the two antibody method. Five animals were killed at each of the following times: 0, 24, 48, 72 and 96 hrs. The blood glucose concentrations were three times greater than the zero-hour values at each of the latter time periods. In spite of the hyperglycemia at twenty-four hours, there was only a slight decrease in the pancreatic insulin content at this time. Thereafter, the insulin content of pancreatic extracts decreased progressively with time, and at ninety-six hours the insulin concentration was less than 10 per cent of the zero-hour value. The immunoassayable insulin concentration of the plasma did not increase as the pancreatic insulin decreased. These findings suggest that alloxan damaged beta cells did not release their insulin in response to hyperglycemia but that the insulin was destroyed within the beta cell.