A 44-year-old nurse with a 12-year history of systemic lupus erythematosus developed a schizophrenia-like psychosis due to cerebral lupus. Prednisolone in doses up to 200 mg daily was ineffective. Levels of immune complexes by the Raji cell assay were greatly increased in serum and cerebrospinal fluid. Plasma exchange was performed on 4 occasions over 4 days. Three days later, there was a marked and sustained improvement in the mental state, the psychosis resolved and tests of psychological function and electroencephalographic abnormalities improved. There was a corresponding decrease in levels of immune complexes and in titres of anti-neuronal antibody. Five months later, several serological indices had risen to pre-plasmaphaeresis levels except for the level of immune complexes. The patient remained in clinical remission. This case provides further evidence that high levels of circulating immune complexes may be a determinant of cerebral lupus and that plasmaphaeresis may be of lasting benefit in this disease.