We investigated the relationship between disease activity and total IgE concentration in the sera of patients with active systemic lupus erythematosus (SLE). In addition, the prevalence of personal and family history of allergic rhinitis and asthma were examined with a questionnaire and immediate skin tests for common inhalant allergens in 24 patients in remission. In the 20 patients with active disease, we found that IgE concentration was significantly higher during the periods of active disease than the periods of remission. This elevation was not associated with an elevation in total serum IgG concentrations. The increase in IgE concentration during disease activity in patients with active nephritis was significantly higher than in patients without nephritis. Of the 24 patients in remission, only one reported allergic rhinitis, and two had positive skin tests for inhalant allergens. We concluded that, although patients with SLE do not have an increased rate of atopic disorders, serum IgE rises during disease activity and is associated with active nephritis. This phenomenon suggests that IgE may be involved in the pathogenesis of SLE, particularly in patients with nephritis.