A method is described for the large isolation of highly purified human growth hormone for therapeutic use. The hormone was extracted from frozen pituitary glands under mildly alkaline conditions. Purification was effected by gel filtration and ion-exchange chromatography. The final product was pyrogen-free and had a potency of 2·5 i.u./mg measured by bioassay against the current international standard. The yield of growth hormone/gland was approximately 5 mg.