Precise and specific radioimmunoassays have been developed to quantify IgG4 and IgG4 antibodies. A community survey has demonstrated that men have significantly higher total serum IgG4 levels than women: geometric mean values of 0.581 mg/ml versus 0.302 mg/ml. This sex difference was extended to total IgE values. Circulating levels of IgG4 antibodies against foods, especially egg and milk, were normally higher than those against the three most common U.K. inhalant allergens--grass pollen, house dust mite and cat epithelium.