The thermally induced changes in human IgE was investigated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. When the IgE (1 mg/ml) was heated at 56 degrees C for several hours in the absence of sodium dodecyl sulfate, it gave aggregated forms that could be reduced completely to heavy and light chains with dithiothreitol. On the other hand, in the presence of sodium dodecyl sulfate (0.1%), the IgE was changed by heating to five components with small mol. wts dependent on temperature and pH. This phenomenon was observed also in mouse monoclonal IgG1, but the degree of change was considerably lower than that of human IgE. The five components obtained from the heat-treated IgE (LHHL) were identified as LHHL, HL, H, LL and L. These results show that the thermally induced changes in human IgE are dependent on the exchange of its intra- and inter-disulfide bonds.