A mouse monoclonal IgA antibody (A008), anti-blood group A antigen, was shown to dissociate into heavy (H) and light (L) polypeptide chains under non-reducing conditions. The dissociation occurred in the presence of 0.2% sodium dodecyl sulphate (2 h at room temperature) or at elevated temperature (1 h at 70 degrees C). The free H and L polypeptide chains could be separated in SDS-polyacrylamide gel electrophoresis or by gel filtration in the presence of SDS. The dissociation of IgA (A008) antibody into heavy and light polypeptide chains was reversible, since the fractions containing gel filtration-isolated chains, after removing the detergent, pooling together and incubation at 4 degrees C created again the immunoglobulin molecules with activity close to the native value. Similarly, the same IgA antibody heated at 70 degrees C for 1 h recovered its antibody activity after keeping at 4 degrees C. Three other mouse monoclonal IgA antibodies showed the same ability to dissociate into heavy and light polypeptide chains after exposure to SDS or elevated temperature, which suggests that this outstanding property is a characteristic feature of the mouse monoclonal IgA antibodies and it comes out from the lack of H-H, L-L and H-L interchain disulfide bonds in these molecules.