The human IgA2-λ myeloma protein Fel consists of covalent dimers and monomers which are partially self-associated. Affinity chromatography of this protein on staphylococcal protein A-Sepharose revealed that approximately 8% of the protein was retained and eluted by acid buffer. Although retained protein Fel was highly aggregated, in the presence of dissociating agents mostly monomeric form was found. Affinity rechromatography and electrophoresis of both fractions from affinity chromatography revealed that the retained fraction possessed substantially higher affinity for SpA than did the nonretained one. This could be due to the multivalency of protein Fel aggregates. © 1987.