Most chemotherapeutic agents are myelosuppressive and immunosuppressive. Consequently their use greatly increases a patient's susceptibility to infection. Neutropenia creates greater risk than lymphopenia and is a particular problem in patients with acute leukemia who are treated with combination chemotherapy. Chemotherapy is less immunosuppressive if given in short intensive courses rather than continuously. Continuous therapy causes severe depression of antibody production and inhibition of delayed hypersensitivity reaction.