Serum IgE concentrations were determined according to the radioimmunosorbent technique (RIST, Phadebas) on 116 adult patients with atopic dermatitis of varying severity and activity. Geometric mean IgE levels of patients with atopic dermatitis were significantly higher compared with the mean level of ninety-three non-atopic adult subjects without parasitic infestation. Severity of the atopic dermatitis was highly correlated to the levels of serum IgE. Severe chronic cases with ever-recurrent exacerbations show the most extreme values. In the moderate forms of atopic dermatitis, coexistent bronchial asthma causes a greater increase in the IgE values. Among the mild or abortive forms, higher IgE levels were found in cases with allergic rhinitis than in the cases with‘pure’atopic dermatitis. Other findings in connection with IgE in atopic dermatitis are summarized. The pathogenetic significance of IgE in the cutaneous changes is briefly discussed.