Dialysed extracts of fresh or old pigeon excreta comprise very heterogeneous mixtures of soluble proteins, glycoproteins and polysaccharides. Because these unfractionated mixtures of components cause precipitate formation in agar gel with each human serum sample, crude extracts constitute unsuitable sources of antigens for the in vitro diagnosis of pigeon-breeder’s disease. Simple gel filtration on columns of Sephadex G-150 permits easy separation of the aselective antigens, which are mainly composed of high-molecular-weight heteropolysaccharides.