Eight-hundred ninety-five previously untreated acute lymphoblastic leukemia (ALL) patients were entered on a protocol designed to provide results of selected immunologic tests. At diagnosis, delayed hypersensitivity tests with four antigens (tetanus, diptheria, candida, and SKSD), immunoglobulin levels, tests for serum inhibition to phytohemagglutinin-stimulated lymphocyte blastogenesis, and HLA-A, B, and C typing were performed. Although delayed lymphocyte blastogenesis have been reported previously to be abnormal in ALL, we did not find them to be associated with disease outcome. Thirty percent of the patients had reduced levels of one or more immunoglobulins. The frequency of remission was less in those patients with decreased IgG and IgA. IgA and IgM showed prognostic importance in remission duration, and all three fractions appeared to have prognostic significance for survival duration. Although none of the HLA types appeared to be associated with significantly increased or decreased success in remission induction, patients with antigens A28 or B12 and patients bearing lymphocyte A11/B35 had shorter remissions. our results indicate that the immunologic factors studied, hypogammaglobulinemia and certain HLA antigens may be related to disease control and outcome in ALL.