We have demonstrated the efficacy of therapeutic pheresis in a number of rheumatic diseases, especially rheumatoid arthritis (RA). Ten of 12 patients with RA went into remissions averaging 4 months. These patients were pheresed 20 times over 11 weeks in a tapering fashion on a Haemonetics Model 30 Blood Processor. Clinical remissions were sustained even though serologies, immunoglobulins, immune functions, sedimentation rates, and circulating immune complexes returned to their pre-pheresis baseline by pheresis number 20. All these patients were taking gold or D-penicillamine concurrently, but neither of the 2 patients who failed to respond was on these agents. Plasmapheresis was just as effective as lymphoplasmapheresis. It is theorized that removal of a plasma factor that modulates lymphocyte or neutrophil function produces remissions in RA and that long-acting drugs (e.g., gold or penicillamine) are able to prevent its continued production and produce a sustained remission.