Human chorionic gonadotropin (HCG) with a biological potency of 19,000 IU/mg has been obtained by a combination of procedures involving gel filtration on Sephadex G-100 and chromatography on SE cellulose. However, these biologically active preparations are not immunochemically pure. A component of serum was always present and at times a component of urine was also detected; neither were associated with pregnancy. Amino acid and amino sugar analyses were determined on three partially purified materials of different biological potencies and the significant changes are noted in the text. Reduction of HCG preparations with 2-mercaptoethanol destroyed both biological and immunological activity of HCG but did not affect the immunological activity of the extraneous serum and urinary components. Chymotrypsin treatment of a purified fraction of the hormone drastically altered the immunoelectrophoretic properties of HCG, but had little effect on the ability of the material to inhibit agglutination. Fractionation of a sample of the purified material on Sephadex G-100 after enzyme digestion did not aid in the isolation of immunologically reactive, homogeneous material.