A high-affinity monoclonal antidigoxin antibody, produced by somatic cell fusion, was amplified by the formation of ascites. Purification from ascites was accomplished by affinity chromatography by passing the ascites over a digitoxin-amine-agarose column. Affinity-purified antidigoxin antibody was coupled to a pellicular microbead at concentrations of 10, 25, 50, and 100 mg/g bead. The immobilized antibody was characterized for binding affinity, for specificity to other cardiac glycosides, and for binding capacity. There were no changes in the binding affinity observed for the immobilized antibody when compared to that of the antibody grown in culture media. Binding capacities for the immobilized antibody were decreased from calculated theoretical values. Saturating the microbead with increasing concentrations of antibody lowered the binding efficiency of the antibody from 32 to 22% of theoretical values. Attempts to improve the binding capacity by immobilizing antibodies to the microbead at the immunoglobulin carbohydrate by periodate oxidation were unsuccessful. These data demonstrate that antidrug antibodies immobilized on solid supports remain functional and may have the capability of removing drug from biological fluids passed over the support.