Patch testing with crude dust mite extracts after removal of homy layers was performed on normal-appearing skin of 11 adult patients with atopic dermatitis and high mite-specific IgE antibody scores. Positive skin reactions were observed in 9 subjects. Skin biopsy specimens were obtained from positive reaction sites at 2, 6, 12, 24, and 48 hours after allergen challenge and subjected to histologic studies and extraction of messenger RNA (mRNA). Perivascular infiltration of small mononuclear cells began at 2 hours and was followed by eosinophilic infiltration at 6 hours, and the number of eosinophils continued to increase at 24 and 48 hours. In addition to the increased expression of IL-4, IL-5, and tumor necrosis factor-alpha mRNA during the time course detected by reverse-transcription polymerase chain reaction, mRNA of IL-6 and IL-7 was also up-regulated. After the removal of test patches with mite allergen, the number of eosinophils started to decrease in a time-dependent manner. Histopathologic findings at 48 hours after removal showed lymphocyte-dominant infiltration intermingled with occasional eosinophils. These mite allergen patch test reactions may provide a useful model for studying the pathogenesis of atopic eczema, especially with regard to the initiation of eosinophil infiltration and the alternative increase in lymphocytes.