During a series of studies on the involvement of house dust mite antigens in 183 cases of atopic dermatitis, we observed an improvement in two patients following the removal of mites from their environment by means of a thorough housecleaning and replacement of the mattress. Both patients manifested the typical clinical skin lesions of atopic dermatitis and had similar laboratory findings. Although the serum IgE concentrations and specific IgE to Dermatophagoides pteronyssinus and Dermatophagoides farinae were each relatively low, the results of patch tests with these antigens were positive. Thus, a regimen aimed at reducing the presence of house dust mites can produce clinical improvement in a subset of patients with atopic dermatitis who show contact hypersensitivity to mite antigens on skin testing, but negative results on IgE (RAST; radioallergosorbent technique) testing.