Cell-mediated immunity was studied in patients with atopic dermatitis. Tuberculin skin tests were performed on 70 patients and on 18 controls. The patients with "severe dermatitis" and those with high IgE levels were hyporeactive. Lymphocyte transformation tests were carried out in 33 patients and 21 controls. This showed that the patients were hyporeactive to PPD and herpes simplex antigen and this was most prominent in the patients having high IgE values. However, there was no clear, statistically significant difference between patients and controls with regard to their in vitro response to PHA.