THE recent isolation of human growth hormone from pituitary glands collected at autopsy has been of major importance in the investigation of human pituitary physiology.1 , 2 Metabolic studies have confirmed the remarkable anabolic and growth-promoting actions of this hormone in man,3 , 4 in contrast to the negative or equivocal clinical results previously observed with bovine growth hormone. The unusually high species specificity of human growth hormone has been further demonstrated by immunologic studies, in which antigenic similarity and biologic effectiveness have closely paralleled one another among various mammalian species.5 An assay taking advantage of immunologic specificity was first reported by Read and . . .