To determine the significance of changes in serum antineuronal antibody levels in systemic lupus erythematosus, 9 patients who had a rise and 11 patients who had a fall in neuronal antibody titre over a mean duration of 2.1 years (range 0.25-5.2) were identified. These changes were examined in the light of concurrent changes in other serological variables, overall disease activity, neuropsychiatric disease and neuropsychological tests. Changes in antineuronal antibodies were frequently associated with concurrent changes in anti-DNA antibodies and overall disease activity. When neuropsychiatric disease or cognitive dysfunction were present, their course showed a close correlation with changes in antineuronal antibody levels. The results support the association between antineuronal antibodies and neuropsychiatric-systemic lupus erythematosus, but suggest that their measurement will provide useful information of disease status in only a subpopulation of patients.