Abstract: A clinically active component (TBGH-d) of a tryptic digest of bovine growth hormone (BGH) found to be homogeneous by disc electrophoresis and sedimentation equilibrium and having substantially the same molecular weight and amino acid composition as BGH was separated into two fractions, A-I and A-II, by dextran gel filtration in 50% acetic acid. The amino acid analysis of the A-I and A-II fractions accounted for all the amino acids in the TBGH-d. The biological activity of the A-II fraction was found to be about 10-30% of TBGH-d. This fraction, having a molecular weight of about 5000 and an amino acid content or chain length of 38 amino acids, appears to exhibit human growth hormone-like activity. This fraction also appears to have wider applicability than simply being useful for the acceleration of somatic growth in humans.