To learn whether the removal of immune complexes from the circulation by plasma exchange could effect an improvement in disease activity in rheumatoid arthritis (RA) patients, we performed a controlled study of 20 patients with severe progressive disease which had not responded to previous therapy. Ten patients (Group 1) were hospitalized, continued on their regular antiinflammatory medication, and given a graded course of physiotherapy. A further 10 patients (Group 2) received the same treatment as the first group with the addition of a concurrent course of plasmapheresis. Clinical measurement of disease activity after treatment revealed little difference between the two groups with a statistically significant improvement in four measures in Group 1 and in five in Group 2. Laboratory studies suggested that the intensity of plasma exchange was sufficient to remove circulating immune complexes in these patients. Our results confirm that hospitalization in itself is of benefit in the treatment of acute exacerbations of rheumatoid arthritis. The marginal improvement achieved by the addition of plasma exchange in the management of these patients (despite the removal of circulating immune complexes) makes its short-term use of questionable value in the treatment of severe rheumatoid arthritis.