Since August of 1988, we have treated seven CTCL patients with extracorporeal photochemotherapy, including two with tumor-stage mycosis fungoides (MF) showing mucinous degeneration, two with plaque-stage MF, and two with erythrodermatous MF. One was withdrawn just after the first trial. For each patient, the phenotypes of peripheral blood lymphocytes were analyzed by flow cytometry in terms of the percentages of OKT11, OKT3, OKT4, Leu9, OKT8, B1, Tac, OKT9, OKIa1, Leu7, Leu3a/4B4, and Leu3a/2H4 cells. These parameters were compared with the clinical responses according to skin score. The two patients with tumors died, but the five patients without tumors did not. Three of the 6 patients responded to the treatment. Side effects that are often associated with standard chemotherapy, such as bone marrow suppression, gastrointestinal symptoms and hair loss, were not observed. One cardiovascular event (1 patient) occurred. No significant changes in T-cell subsets were seen during the course of therapy. These preliminary data suggest that extracorporeal photochemotherapy may be effective for CTCL other than tumor-stage MF.