By simultaneous spectroscopic measurements (absorbance, light scattering, fluorescence and circular dichroism) the temp-dependent behavior of a cryoglobulin, the mouse monoclonal immunoglobulin G to N-acetyllactosamine, has been observed. The results show that a hapten-induced conformational change in the structure of a cryoglobulin can accompany its intermolecular association. This association of the immunoglobulin increases after hapten saturation of its two antigen-combining sites.