Rosalyn S. Yalow and Solomon A. Berson developed an immunoassay method for measuring endogenous plasma insulin in humans. This method uses the competitive inhibition of insulin binding to antibodies to determine insulin levels. The technique involves labeling insulin with iodine-131 and using guinea pig antisera to detect insulin. The method allows for the detection of very low insulin concentrations, down to a fraction of a microunit. The study describes the preparation of labeled insulin, the immunoassay procedure, and the results of insulin measurements in various subjects, including nondiabetic and early diabetic patients, as well as those with islet cell tumors or leucine-sensitive hypoglycemia. The results show that insulin concentrations in diabetic subjects during glucose tolerance tests are higher than in nondiabetic subjects, with the peak insulin concentration occurring later in diabetics. The study also highlights the importance of using a highly purified insulin standard and the need to account for potential errors due to plasma damage. The immunoassay method is compared with other methods, and it is found to be more sensitive and specific. The study concludes that the immunoassay technique provides reliable results that are consistent with other methods, and that the findings support the use of this method for measuring insulin in plasma. The study also discusses the implications of the findings for understanding the pathogenesis of diabetes and the role of insulin in glucose metabolism.Rosalyn S. Yalow and Solomon A. Berson developed an immunoassay method for measuring endogenous plasma insulin in humans. This method uses the competitive inhibition of insulin binding to antibodies to determine insulin levels. The technique involves labeling insulin with iodine-131 and using guinea pig antisera to detect insulin. The method allows for the detection of very low insulin concentrations, down to a fraction of a microunit. The study describes the preparation of labeled insulin, the immunoassay procedure, and the results of insulin measurements in various subjects, including nondiabetic and early diabetic patients, as well as those with islet cell tumors or leucine-sensitive hypoglycemia. The results show that insulin concentrations in diabetic subjects during glucose tolerance tests are higher than in nondiabetic subjects, with the peak insulin concentration occurring later in diabetics. The study also highlights the importance of using a highly purified insulin standard and the need to account for potential errors due to plasma damage. The immunoassay method is compared with other methods, and it is found to be more sensitive and specific. The study concludes that the immunoassay technique provides reliable results that are consistent with other methods, and that the findings support the use of this method for measuring insulin in plasma. The study also discusses the implications of the findings for understanding the pathogenesis of diabetes and the role of insulin in glucose metabolism.