Prompted by recent observations that the thymus exerts an important regulatory influence over IgE antibody production in lower species, we conducted studies of immune function in 21 patients with atopic eczema to seek evidence for a similar relation in man. Skin tests for delayed hypersensitivity to Candida albicans and streptokinase-streptodornase (SK-SD) revealed a striking degree of anergy that correlated with the severity of the eczema. A correlation was also noted between the extent of the dermatitis and the magnitude of the serum IgE concentration. Other immunologic abnormalities did not appear related to the severity of eczema put pertained to the group as a whole. These included significantly (p = less than 0.0001) lower mean percentages of spontaneous sheep erythrocyte (E) or T cell rosettes and of rosettes with neuraminidase-treated sheep erythrocyte (En) rosettes, and significantly lower in vitro lymphocyte responsiveness of the mitogens concanavalin A (p = 0.0013) and poleweek mitogen (p = 0.0002) and to Candida antigen (p = 0.0017) than in normal subjects. Responses to phytohemagglutinin and tetanus toxoid were also depressed but differences were not statistically significant. An increased percentage (p = 0.0324) of peripheral blood B lymphocytes bearing the complement receptor was noted, but, except for a slight increase in lymphocytes bearing IgD, percentages of lymphocytes bearing other immunoglobulins (including IgE) were not elevated.