Diseases such as allergic asthma and rhinitis, atopic dermatitis, and certain helminth infections are all characterized by elevated levels of serum IgE. At least two mechanisms could be operating in vivo causing the elevated IgE levels in the above-mentioned diseases: Upregulation of enhancing factors such as interleukin (IL-)4, or downregulation of suppressing factors such as interferon γ (IFN-γ). We have compared two different patient groups (inhalation allergy and atopic dermatitis patients) with nondiseased subjects with normal IgE levels and found strikingly different cytokine profiles in the two groups. Whereas patients with inhalation allergy demonstrate increased IL-4 and IL-5 production but normal IFN-γproduction, patients with atopic dermatitis show normal IL-4/IL-5 production but a markedly poor capability of IFN-γ production. It has been demonstrated that leishmaniasis patients also have increased capacity to produce IL-4, and in this respect they resemble patients with a specific inhalation allergy. Atopic dermatitis and inhalation allergy have been regarded as common manifestations of atopic disease. We propose, however, that the dysregulation of IgE synthesis varies between the two types of diseases and that these two forms may have different inflammatory consequences.