Three major polypeptides of 34, 48 and 50 kDa which appear to copurify with 1,3-beta-glucan synthase activity were isolated by glycerol gradient centrifugation of Chaps-solubilized proteins from the fungus Saprolegnia monoica. The antiserum produced against the 34-kDa polypeptide revealed by protein immunoblotting that this polypeptide copurified with 1,3-beta-glucan synthase during enzyme purification. This antiserum adsorbs the enzymatic activity as well as the 48- and 50-kDa polypeptides. These results indicate that the 34-kDa peptide is a component of the multisubunit protein complex involved in 1,3-beta-glucan synthase activity.