The influence of age and sex has been evaluated in 326 allergic patients on the following parameters: total serum IgE concentration, serum concentration of specific IgE antibodies against seventeen common allergens, mean number of positive allergens, absolute numbers of circulating eosinophils, corticosteroid dependence and response to sodium cromoglycate (DSCG). The results indicate that age and sex significantly influence the IgE antibody production in these patients. The data strongly suggests the appearance during ageing of a progressive natural desensitization. This contrasts with the increased frequency of corticosteroid-dependent cases during ageing. There is an inverse relation between age and response to DSCG therapy.