Radioimmunoassay methods were modified for insulin(IRI), C-peptide (IRCP) and glucagon (IRG) in the clinical investigation on normal subjects and 38 patients with non-insulin-dependent diabetes mellitus (NIDDM). In the control group, the peaks of glucose and IRI appeared 1 hour after glucose was taken. IRCP peak, however, appeared 1 hour later. IRG showed its maximum value on fasting and then reached its lowest point at the second hour after glucose loading. The authors' interests were focused on the changes of blood glucose, IRI, IRCP, and IRG in oral glucose tolerance test (OGTT) before and after Ke-Tang-Ling (KTL) was administered in NIDDM. The results demonstrate that the glucose levels and undercure areas at various phases in OGTT were significantly decreased (P less than 0.01) in comparison of before and after the treatment with KTL in NIDDM (including obese and non-obese groups). In non-obese group, however, IRI, IRCP, and their undercure were remarkably increased (P less than 0.01). In obese group their values were decreased. It suggests that KTL plays a therapeutic role in decreasing blood glucose in non-obese NIDDM. The mechanism involved in this process may be related to its stimulating effect. IRG levels were decreased also (P less than 0.01) after the treatment with KTL in both obese and non-obese NIDDM, suggesting an inhibitory effect on glucagon secretion from alpha cells in pancrease.