High-affinity (Ka = 3.0 X 10(8) M-1) monoclonal antidigoxin antibodies were covalently coupled to Sepharose CL-6B, Bio Gel A5m, Affi-gel 15, and agarose:polyacrolein microsphere (APAM) beads. Antibody immobilized to these supports was characterized in its ability to remove digoxin in vitro from biological fluids. Equilibrium binding studies of digoxin in plasma revealed that antibody coupled to Sepharose, Bio Gel, and Affi-gel 15 retained 38-42% of theoretical binding capacity, whereas antibody coupled to APAM beads retained only 13%. Increasing flow rates from 0.5 to 5.0 mL/min across antibody immobilized to APAM beads decreased the removal of digoxin from plasma from 90 to 55%. In comparison, no decreases were observed in the amount of digoxin removed from plasma as the flow rates were increased across antibody immobilized to the other agarose supports. Antibody coupled to Affi-gel 15 was used for in vivo extracorporeal hemoperfusion studies. These studies indicated that although 5-20% of the total dose was removed from three guinea pigs, plasma digoxin levels were not lowered when compared with preperfusion concentrations. In addition, antibody columns which were reused following regeneration with glycine:HCl, pH 2.5 revealed that 80% of the original antibody activity was lost after two hemoperfusions. Hematological parameters were unchanged with the exception that platelets were significantly decreased following the 3-h perfusion study. These data indicate that immobilized antidigoxin antibodies were able to remove digoxin from the circulation, and immunoaffinity hemoperfusion may be a viable means of removing substances from blood.