The Childrens Cancer Study Group is a national cooperative group of institutions comprised of multidisciplinary groups of pediatric oncologists, hematologists, radiotherapists, surgeons, immunologists, pathologists and biostatisticians and dedicated to the objective of improving the prognosis and survival of children with leukemia, lymphomas and solid malignant tumors through controlled, clinical trials employing multimodal therapy. In addition to large scale Phase III studies in leukemia and other cancers, the group has active Phase II protocols utilizing newer investigational drugs. Natural history of disease, immunotherapy, special studies related to the biology of disease, treatment complications and dissemination of newly acquired knowledge on cancer diagnosis and treatment to the medical community at large are other objectives of the Group. Currently, patients with the following diseases are being entered on group protocols, ALL (CCG 161-162-163), AML (CCG 251), non-Hodgkin's lymphoma (CCG 541), medulloblastoma (CCG 942), high grade astrocytoma (CCG 943), brain stem glioma (CCG 944), Wilms' tumor III (CCG 441), retinoblastoma, rhabdomyosarcoma, neuroblastoma, Ewing's sarcoma, hepatoma, gonadal and germ cell tumors, histiocytosis and osteogenic sarcoma. Special studies relating to infectious disease complications and natural history are under investigation. Active protocols exist for retrieval therapy in relapsing patients with leukemias.