The expression of intercellular adhesion molecule-1 (ICAM-1) on keratinocytes was studied in skin specimens of patch- or scratch-test using Dermatophagoides farinae (DF) antigen in atopic dermatitis (AD). Positive patch test reaction showed exocytosis of lymphocytes and focal expression of ICAM-1 on keratinocytes. Similar lymphocyte infiltration and keratinocyte expression of ICAM-1 were observed in tape-stripped skin which was subjected as the control. In addition, focal ICAM-1 expression on keratinocytes was also observed without exocytosis of lymphocytes. By scratch-test with DF antigen, ICAM-1 expression on keratinocytes was observed in eight out of eleven patients. One specimen showed ICAM-1 expression in spite of the absence of exocytosis of lymphocytes. Two out of three specimens from negative scratch-test sites with control liquid (mixture of equal amount of saline and glycerine) showed ICAM-1 expression in a similar manner to that of the positive scratch tests. In normal control skin, patch-test sites showed focal and weak expression of ICAM-1. Normal appearing skin of AD also showed no ICAM-1 expression. Therefore, in patients with atopic dermatitis, keratinocytes may express ICAM-1 prior to infiltration of lymphocytes into the epidermis and this expression might be induced not only by cytokines produced by lymphocytes but also by mechanically injured (tape-stripped or scratched) epidermal cells.