METHODS Antiserums were obtained from insulin-treated diabetic and schizophrenic subjects generally at least 24 hours and frequently many weeks following the last injection of insulin and were stored frozen or at 40 C. for weeks or months prior to use.

Insulin-I131 was prepared from crystalline beef insulin'with specific activities of 10 to 100 mc. per mg. Methods employed in preparation and in protection of the insulin against extensive radiation damage have been described (2, 3). However, because of the extremely high specific activities of the preparations and the trauma incident to the labeling procedure, storage and dilution, occasionally as much as 10 per cent of theinsulin-I'3l was damaged by the time of use. Recent preparations, with which the bulk of the quantitative data has been obtained, have uniformly contained less than5 per cent damaged com-ponents.