Biosynthetic glucagon (GL-G) produced by recombinant DNA technology with transformed yeast strains is already available for clinical use. We studied the effects of 1 mg GL-G injection on plasma glucose level and hypoglycemic symptoms in 38 diabetic patients treated with insulin or oral hypoglycemic agents during spontaneous hypoglycemic episodes. In both intramuscularly and intravenously administered GL-G groups, plasma glucose significantly increased from 58.1 +/- 11.4 to 113.2 +/- 6.9 mg/dl (i.m., n = 17, P < 0.01) and from 76.4 +/- 4.4 to 125.7 +/- 5.9 mg/dl (i.v., n = 15, P < 0.01), respectively 20 min after the administration and the symptoms due to hypoglycemia subsided promptly after the injection of GL-G in 27 cases. The hyperglycemic effect of intramuscularly injected GL-G was more potent and long-standing than when intravenously injected, particularly in insulin-dependent diabetic (IDDM) patients. Neither significant changes of antibody levels against yeast proteins nor serious adverse effects were observed after GL-G administration. Biosynthetic glucagon is safe and useful for the treatment of hypoglycemia developing in diabetic patients.