The purpose of this project is to participate in multi-institutional cooperative trials whose objective is to improve survival of pediatric tumors. A major emphasis will be to further refine the success that has been achieved in the treatment of acute lymphoblastic and undifferentiated leukemia by treating according to front end prognostic factors. Further proposals include Phase I and II studies of new chemotherapeutic agents and Phase III studies to develop new approaches that will improve survival of children with bone tumors, neuroblastoma, brain tumors and Wilms' tumor.