The primary goal of this study is the increase in knowledge of treatment methods for patients with pediatric malignancies. The specific aims are the collaboration with other investigators in the Southwest Oncology Group with entry of patients on cooperative protocols so that information can be obtained on a number of patients too small to be obtained at any individual institution in patients with these pediatric tumors. Patients will be studied in a scientific fashion. The majority of studies will be prospective, randomized trials of conventional therapy versus some innovative aspects of treatment. In some tumors, where no adequate conventional therapy exists, historical controls may be employed. This project represents a collaborative effort between the departments of oncology, pediatrics, surgery and radiotherapy. The principal studies will involve the evaluation of new modalities of therapy and new drugs in cancer patients. Excellent patient care and detailed record-keeping will be required. Glucocorticoid receptor levels will be measured in patients' leukemia cells and these will be correlated with other marker studies and with clinical responses.