Highly purified preparations of Human Chorionic Gonadotrophin (HCG), with potencies up to 18 800 IU/mg, were obtained from material containing about 1500 IU/mg, by using a fractionation with ethanol, CMSephadex chromatography and gel filtration with Sephadex G-100. Starch gel electrophoresis revealed that the most potent preparation still contained three components, while certain other fractions with much lower potencies were found to be homogeneous. Evidence is presented for the presence of various HCG components differing from each other in biological potency, electrophoretic mobility and sialic acid content. Within this material, components with higher electroporetic mobilities and higher sialic acid contents showed higher biological potencies. The molecular weight estimated in the absence of calcium ions was 62 000 ± 1000.