Cell-mediated immunity to bacterial antigens was studied by intradermal testing, and to contact antigens (cosmetics, environmental chemicals and topical medicaments) by patch testing in 270 children with atopic dermatitis. The incidence of delayed-type immune cutaneous reactions in these patients was lower than in the controls. Contact allergy is a rare finding in the first 4 years of life but its incidence increases subsequently. In subjects with atopic dermatitis the incidence of sensitization by contact with allergens contained in topical medicaments proved to be lower than in subjects with eczema of other types. The data collected points to a reduced cell-mediated immune reactivity in a proportion of subjects with atopic dermatitis.