OUTLINE: This is a randomized, double-blind, placebo-controlled, multicenter study. Patients are stratified according to disease and duration of planned vincristine-containing treatment (Wilms' tumor or rhabdomyosarcoma with treatment planned for ≥ 9 consecutive weeks [stratum 1] vs acute lymphoblastic leukemia or non-Hodgkin's lymphoma with treatment planned for ≥ 4 consecutive weeks [stratum 2]). Patients are randomized to 1 of 2 treatment arms.