Fragments produced by cyanogen bromide cleavage of human secretory IgA were fractionated before and after the splitting of disulfide bonds on Sephadex G 200 columns in 5 M guanidine/HCl. By electrophoretic, antigenic, amino acid, and carbohydrate analyses of individual fractions it was revealed that J chain was released as a result of cyanogen bromide cleavage. Secretory component remained associated with a large fragment(s) of α chain (approximately 80% the size of the original α chain) to which L chains were also linked. Data indicate that J chain and secretory component are linked to different cyanogen bromide fragments of the α chain(s) and are not mutually connected by disulfide bonds. Although J chain might mediate the binding of secretory component through a disulfide bond interchange reaction, the J chain is not involved in direct bridging between secretory component and polymeric IgA molecules.