Lymphocyte subsets measured by Ortho-mune on OKT 3, OKT 4A, OKT 8, OKT 10, OKT 11, OKM1, OKB 7, OKB 2 and OKDR were observed before and after chemotherapy on patients with gastrointestinal, lung and hematopoietic malignancies. Almost all patients showed decreased T-cell function expressed by OKT 11 or OKT 3 and suppressor, helper T-cell function expressed by OKT 8 and OKT 4A. In some patients improvement of T-cell function were observed with clinical response and in such cases life span seemed to be longer as expected, and it is supposed that during cancer chemotherapy improvement of T-cell function expressed by OKT series may be important prognostic factors.