Abstract A method is described whereby the extent of interaction between antigen and purified antibody solutions can be quantitatively determined. An immune globulin solution, prepared from horse antisera to human albumin, was admixed with largepore spacer gel in polyacrylam ide disc electrophoresis. Albumin, migrated in this system was, in part, retarded due to combination with antibody and subsequent exclusion of the complexed material from the small-pore separation gel. The interaction was quantitated by comparing the densitometric evaluation of the stained protein bands of antibody-reacted systems with samples in which the immune globulin was omitted. This method can be used to characterize the immunologie reactivity of various immune globulins in addition to permitting more detailed analyses of antigenic materials.