Biphasic skin reaction with peak response at 1 and 24 h with prominent mast cell degranulation was induced by intravenous application of a monoclonal anti-DNP IgE antibody and subsequent skin test. This reaction was hapten-specific and mast-cell-dependent because no reaction was observed when oxasolone was used as an elicitation antigen or skin test was elicited in genetically mast-cell-deficient mice (W/Wvv). A partial spongiotic reaction and mononuclear cell infiltration into the epidermis were observed in mice with hyperplastic epidermis induced by topical retinoic acid. Cotransfer of DNFB-sensitized lymph node cells with anti-DNP IgE antibodies failed to enhance the skin test reaction in unsensitized mice. These results suggest that, to some degree, IgE antibody may play some role in the development of eczematous skin lesions in the rodent system without the involvement of cellular hypersensitivity.