In an uncontrolled clinical trial the effects of plasma-exchange (PE) on the capacity of the serum to solubilize circulating immune complexes were studied in patients with active systemic lupus erythematosus. Four patients were treated with immunosuppressive therapy alone, while others were also treated by PE over a period of four to seven weeks. Plasma was replaced by fresh frozen plasma in the final part of each procedure. All patients showed evidence of clinical improvement at the time of treatment. Furthermore, PE was demonstrated to reduce drastically the number of relapses. An improvement of the capacity of solubilize immune complexes in vitro associated with a persistent fall in the levels of the circulating immune complexes was observed in patients treated with PE. This suggests that fresh frozen plasma improves the clearance of immune complexes and reduces the frequency of relapses. In our experience, clinical improvement and/or resolution of the symptoms seems to be related to the decrease in serum immune complex levels, while clinical relapses seem to parallel the behaviour of complement-mediated solubilization.