In the latter part of the 1950's, Berson and Yalow demonstrated the presence of insulin antibodies in insulin resistant diabetic patients. These patients had been treated with other than species specific insulin preparations and presumably, had made antibodies against the foreign hormone. It was found that these insulin antibodies had the ability to competitively bind insulin which had been labeled with 1311 as well as unlabeled insulin. From these observations, Berson and Yalow developed the first radioirnrnunoassay (RIA) in 1959 ( 8) and presented a clinically useful method in 1960 (65).