In a group of 10 patients (six with acute lymphatic leukaemia, one patient with Ewing's sarcoma, one patient with lung cancer, one patient with a myeloma and one patient with Hodgkin's lymphogranuloma) treatment with leucocytic growth factors (Neupogen Hoffman La Roche) was started only after the onset of leukopenia. Even after this mode of administration of leucocytic growth factors septic conditions in leukopenic patients were more easily controlled and it was thus possible to complete chemotherapy with planned doses in the planned time interval. In five patients with acute lymphatic leukaemia the leucocytic growth factors participated in the achievement of remission, in patients with myeloma and lymphogranuloma they contributed to marked improvement of the general condition and reduction of the time spent in hospital.