The cutaneous lymphocyte-associated antigen (CLA) has been proposed as a homing receptor for the selective migration of memory T cells into the skin. To investigate the effect of cyclosporine on the expression of CLA of the lymphocytes infiltrated in psoriatic lesions, CLA expression was assessed by the immunohistochemistry(HECA-452 epitope) with skin samples from 9 patients at time sequential(before treatment, 3 weeks, 6 weeks, and 12 weeks after initiation of treatment). CD3+ or CD4+ cells were also analyzed by immunohistochemistry on the same skin samples. Mean CLA expression on the infiltrated lymphocytes was decreased continuously during 12 weeks treatment with a further decrease during 3-6 weeks. CD3+ or CD4+ cells were decreased rapidly during the first 3 weeks of treatment. Although most CLA+ lymphocytes overlap with CD3 or CD4+ cells, cyclosporine could have therapeutic effects by differential decrease of CD3, CD4, or CLA+ cells during treatment period. In conclusion, reflecting the importance of CLA expression on the lymphocytes infiltrated in psoriatic lesion, one of the mechanisms to treat psoriasis may result from selective decrease of CLA+ T cells by cyclosporine in psoriatic lesions. (Korean J Dermatol 2001; 39(3): 280~284)