Type 2 helper T-cell immune responses can be demonstrated in the human atopic disorders atopic dermatitis and allergic asthma/rhinoconjunctivitis. The CD30 (Ki-1) antigen, originally described on Hodgkin and Reed-Sternberg cells, has recently been proposed as a marker of T cells with potent B-cell helper activity producing IL-5 and gamma-IFN, as well as on CD4+ and CD8+ T cells with a Th2 cytokine profile. As a soluble form of CD30 (sCD30) is released by CD30+ cells in vivo, we studied its clinical significance in atopic disorders compared with allergic contact dermatitis and healthy controls. Elevated sCD 30 levels were associated with atopic dermatitis (P < 0.0001), but not with respiratory atopic disorders or allergic contact dermatitis. sCD30 levels in patients with atopic-dermatitis were independent of serum IgE. The particular occurrence of serum sCD30 in patients with atopic dermatitis indicates a special regulatory function of CD30+ cells in this disease.