Reduction and carbamidomethylation of the intrachain disulfide bridges of human growth hormone did not destroy its ability to stimulate weight gain or cartilage metabolism in hypophysectomized rats. The reduced and alkylated hormone also stimulated glucose oxidation in isolated adipose tissue of hypophysectomized rats when added in vitro. When the S-carbamidomethylated hormone was incubated overnight with human plasmin, approximately 95% of the starting material was completely digested, as judged by polyacrylamide gel electrophoresis. The plasmin digest retained the ability to stimulate weight gain, cartilage metabolism, and glucose oxidation. A fraction consisting of two major electrophoretic components was isolated from the digest by chromatography on tsephadex G-50. This fraction possessed the biological properties of the whole digest.