The T cell subpopulation bearing a receptor for the Fc fragment of IgM (T mu) or the Fc fragment of IgG (T gamma) were studied in 12 patients with active atopic dermatitis (AD) and elevated IgE (5678 I.U./ml +/- 1382) and compared with a control group with normal IgE (33 +/- 17). Values for the total lymphocytes and for absolute and relative numbers of total T and T mu cells were comparable in both groups. However, AD patients had markedly reduced relative T gamma levels, 1.8% +/- 0.4%, compared with normals, 10.5% +/- 0.7% (p less than 0.001). The patients also had reduced absolute T gamma levels, 29 +/- 7, compared with 181 +/- 36 (p less than 0.0005). This abnormality was not indicative of allergic disease in general, nor did it appear to be caused directly by serum factors. The T gamma cell deficit did reflect disease activity and correlated inversely with the levels of serum IgE in the AD patients. Thus, patients with active AD and elevated IgE have a selective reduction in circulating T gamma cells.