Growth factors (G-CSF Neupogen Roche i GM-CSF Leucomax Sandoz) have been applied in 133 therapeutic and prophylactic cycles in 88 children with acute leukaemias. GM-CSF and G-CSF were administered subcutaneously or intravenously at a dose of 2 to 8 micrograms/kg for 2 to 28 days. 45 prophylactic cycles had been administered in children with acute lymphoblastic leukaemia in high risk group and in relapses, which caused significant reduction in the number of infections, time of neutropenia and fever. Therapeutic cytokines cycles were applied when the absolute neutrophil count have fallen below 0.5 x 109/l. We observed significant reduction in duration of neutropenia in these cycles. Tolerance of GM-CSF and G-CSF was good. Side effects were not observed.