Summary: A relationship between the molecular configuration of IgG molecules and their immunogenic properties was determined by using Lytron particles for the adsorption of IgG. The change in molecular configuration of IgG molecules was found to be related to the number of groups potentiometrically titrated during adsorption, and an inverse linear correlation was found between the logarithm of the number of firmly attached IgG molecules and the number of groups titrated. The latter value was maximal at pH 6.8 or 5.0 and minimal at pH 8.0 indicating by this titration region that histidine and free amino groups were titrated during adsorption. The immunogenic properties of IgG on Lytron were concentration-dependent. Anti-heavy chain antibodies were formed readily, but with increase in the number of molecules adsorbed per particle the capacity to incite anti-light chain antibodies decreased.