A total number of 608 cycles of G-CSF and/or GM-CSF was applied in 280 patients aged from 6 months to 20 years during neutropaenia associated with chemotherapy of children's neoplasms (NHL-124, NBL-42, RMS-36, Nephroblastoma-18, Osteosarcoma-17, Ewing's Sarcoma-14, Hepatoblastoma-6, Neurofibrosarcoma-6, PNET-5, Medulloblastoma-3, Fibrohistiocytoma-3, Angiosarcoma-2, other - 4). G-CSF - Neupogen (Filgastrim, Hoffman La Roche - 492 cycles) and GM-CSF - Leucomax (Molgramostim, Shering Plough - 116 cycles) were administered 5 mg/kg/day s.c. Forty one children with malignancies (NHL -21 cases, solid tumours -17) treated before cytokines were in use served as a control group. Our study demonstrated that G-CSF and GM-CSF therapy, gives a shorter period of neutropaenia, reduction of the number of febrile days, decreased frequency of infection and shortened its duration.