detection and characterization of monoclonal antibodies to platelet membrane proteins we have devised a solidphase radioimmunoassay for the detection and characterization of monoclonal antibodies directed against platelet surface antigens platelet membrane proteins solubilized with 01 triton x100 were covalently coupled to cyanogen bromide cnbractivated filter paper disks that were than used as the support in antibody binding assays sds page of solubilized membrane proteins taken immediately before and after incubation with activated disks indicated that representative amounts of each membrane protein were bound to the disks either monoclonal or heterologous antiplatelet antibody could be detected on disks that had been prepared using as little as 50 micrograms of membrane protein per 100 disks for the detection of antibody disks were incubated with test sera for 2 h washed and incubated with 125ilabeled antiimmunoglobulin g and the amount of bound radioactivity was determined the sensitivity of the disk assay in detecting monoclonal antibodies was far greater than that of a corresponding radioimmunoassay that used whole platelets as the solid phase by linking other proteins such as fibrinogen or antimouse subclass specific antisera to cnbractivated disks the method was adapted for antibody characterization the sensitivity and ease with which the assay can be performed make this technique most suitable for screening and characterizing monoclonal antibodies