Two major, close molecular weight basic coagulum proteins of freshly ejaculated human semen identifiable on reducing SDS-PAGE, have been isolated together from washed seminal coagulum. The latter was solubilized in urea, followed by reduction and carboxymethylation of disulphide bonds. By high-resolution chromatography on carboxymethy-Sephadex and Sephacryl S-300 using 8 M urea in 0.1M Tris-HCl (pH 7.4) as eluate these proteins were isolated together (purity 99%) with a yield of 10.5%. The molecular weights of the isolated proteins on SDS-PAGE were 75 and 79 kD.