In order to selectively remove pathogenic rheumatoid factors (RF) from plasma of rheumatoid arthritis (RA) patients, a new immunosorbent was developed by immobilizing heat-aggregated human IgG (HAH IgG) on epichlorohydrin-activated agar gel. Different parameters influencing ligand coupling were studied, i.e., ligand concentration, reaction time, temperature and pH. The maximum amount of HAH IgG immobilized on the carrier was 2.7 mg/ml. Adsorption capacity was evaluated by ELISA technique. After incubation of 3.0 ml of RA plasma with 1.0 ml of the adsorbent, the RF IgM, IgG, and IgA were removed by 88%, 74%, and 50%, respectively. The decrease of total immunoglobulins and albumin were less than 7% and 9%. In vitro, perfusion of 10.0 ml plasma at 37 degrees C through 3.0 ml of adsorbent, at a flow rate of 5.0 ml/min for 60 min, resulted in the removal of 49% of RF IgM, 72% of RF IgG and 58% of RF IgA. No leakage of ligand and no decline in adsorption capacity and mechanical strength were observed after steam-sterilization.