The prevalence of naturally occurring anti-IgE autoantibodies was assessed by surveying 387 sera from atopic, nonatopic, and autoimmune patients. A significant number of children (28.5%) and adults (20%) with no history of allergy had high levels of autoanti-IgE. The level of autoantibodies to IgE in children with clinical asthma or atopic eczema was not significantly elevated over normal. Similarly, adults with atopic asthma, allergic rhinitis, or urticaria or sera from individuals with rheumatoid arthritis or systemic lupus erythromatosis showed no significant elevation of auto-anti-IgE. In contrast, 82% of adults with eczema had medium to high levels of auto-anti-IgE and the mean concentration in sera was significantly (P less than 0.01) raised. The relevance of auto-anti-IgE in atopic eczema is discussed.