The immunosuppressive effect of cytostatics, basic therapeutic agents in the treatment of proliferative diseases of the hematopoietic system, and the rising number of children cured from acute leukaemias form together a need to monitor the status of the immune system following cessation of therapy. Surface antigens in lymphocytes from peripheral blood were assessed in 16 children directly after intensive chemotherapy (i.e., after protocol II of the BMF program) and in 25 children 12-13 months following conclusion of acute lymphoblastic leukemia treatment. The results were compared to data obtained from children never afflicted with neoplastic disease. A significant decrease in the average number of lymphocyte subpopulations was noted in the case of the treated children directly after intensive chemotherapy. The average values of lymphocyte subpopulations in children with concluded treatment are within the norm, with the exception of NK and TS lymphocytes.