We describe a patient with C2 deficiency and severe systemic lupus erythematosus (SLE) that did not respond to conventional therapy. Over a period of 45 months, she was given 22 cycles of plasma therapy. For 6-8 weeks after each plasma infusion, there was a full clinical remission of the SLE, and a brief restoration of hemolytic complement activity. However, there were more prolonged increases in the activities of the complement components that are believed to be more directly involved in the clearance of immune complexes. Because of the theoretical risk that the infused complement might enhance inflammatory tissue damage, there has been some reluctance to try plasma replacement therapy in SLE patients with complement deficiency. We have not observed any adverse effects with the long-term use of this treatment, and our experience indicates that this therapeutic approach can be beneficial.