Clinical application of two kinds of glucagon RIA Kits, “Daiichi” and “Dainabot”, was evaluated. Values for glucagon immunoreactivity (GI) assayed by both Kits were satisfactory as regards precision, as confirmed by withinassay, betweenassay, recovery and the dilution effect. The minimum detectable GI concentration was 31.3 pg/ml with “Daiichi”, and 50 pgind with “Dainabot”. The GI levels in fasting plasma of normals (n =16) and of patients with liver cirrhosis (n= 15), chronic renal failure (n=15) and diabetes mellitus (n=45) were assayed by both Kits and another RIA system employing antiglucagon antiserum 30 K. A significant correlation was noted between any two of the three GI assay systems. Using the three assay systems, similar patterns of GI-response after an intravenous injection of 4 g arginine were observed; i.e., rapid increments of GI levels after the injection in both normals (n=6) and diabetics (n=6), and a larger degree of GI increment in the diabetics than the normals. Based on the above results, the glucagon RIA Kits are recommended for plasma GI measurements.