Thirty-seven children and adolescents of several diagnostic entitites (constitutional growth retardation, diabetes mellitus and pituitary insufficiency) were tested with an i.v. bolus injection of glucagon for plasma human growth hormone (HGH) response. Most of the subjects were also tested for the same purpose by the arginine stimulation test, and the data were compared. It was found that i.v. glucagon is a potent stimulus of human growth hormone release. The HGH is released in two peaks, the first one occuring within 30 min, most probably by a direct effect. The second peak occurs after 120 min, most probably as a secondary effect caused by the drop in blood glucose after its initial rise, which is induced by glucagon. The peak concentrations of HGH induced by glucagon, were very similar to those provoked by i.v. arginine in the same subjects.