Psychological and neurological assessment of patients with systemic lupus erythematosus has identified 15 with definite evidence of non-focal cerebral involvement. During the period of neuropsychiatric disease, cerebral blood flow was measured using 15O2 brain scans and sera were tested for the presence of 2 brain-reactive antibodies: antineuronal and lymphocytotoxic antibodies. 12 patients had psychiatric symptoms, while 13 had various neurological abnormalities. Striking abnormalities in cerebral blood flow were observed in 12 patients. All sera contained at least one brain-reactive antibody; 13 contained antineuronal antibody, although there was an inconsistent association between clinical features and antibody titre, while 12 contained lymphocytotoxic antibodies. According to these investigations the nature of the neuropsychiatric abnormalities would depend on both vascular and immunopathogenic mechanisms.