This proposal outlines a program to investigate the variations in T cell and B cell populations of both lymphocytes and monocytes in the serum of pediatric patients with various malignancies. Recent work has shown that T and B lymphocyte populations are balanced at a ratio of 3-3.5:1 in normal peripheral blood and there is a change in the subpopulations or the ratio in various immunodeficiency diseases. Antineoplastic agents, such as steroids and irradiation procedures are also known to alter subpopulation of lymphocytes and their functions. We propose to sequentially study receptors of lymphocytes and monocytes of pediatric patients with neoplasms and leukemia, prior to and during therapy. A close relationship between blood monocytes and tissue macrophages has been reported by the study of M. Feldman. There is increasing evidence that macrophages have a prominent role as "killer cells" in neoplasia. We propose to study monocytes as to their receptors of activated complement and of the Fc fragment of IgG in vitro killing effect in normal and cancer patients. By studying variations in the subpopulations of monocytes and lymphocytes in cancer patients at various intervals during the course of their disease the effect of conventional chemotherapy and irradiation on the balance of immunosurveillance and immunosuppression will be delineated. This information may lead to a more meaningful assay of effectiveness versus toxicity in managing these patients.