Serologic studies were performed on 25 patients with systemic lupus erythematosus (SLE) during 29 acute episodes of central nervous system (CNS) disease. Increased anti-DNA antibody and decreased total serum hemolytic complement activity were observed only in those patients with associated extra-CNS disease manifestations. Patients with isolated CNS disease were otherwise in apparent clinical and serological remission regarding these two indices. No special association of cold-reactive IgM antilymphocyte antibodies was demonstrable in patients with ongoing CNS injury. Of special interest was an increased incidence of anti-Sm antibodies in the patients with CNS dysfunction relative to that in a large group of patients without neuropsychiatric disease. The incidence of anti-RNP was not increased. The data do not support direct involvement in SLE brain injury of either DNA/anti-DNA complexes or of lymphocytotoxic antibodies cross-reactive with brain cells, but do suggest an association of anti-Sm with CNS disease in this disorder.