Bone marrow depression (myelosuppression) in the patient with cancer may result from the disease itself or from its treatment. The consequences of myelosuppression are numerous; the most critical problem that results from leukopenia is infection. Serious clinical consequences follow depression of normal leukocyte function. A clear understanding of the functioning of each type of leukocyte is essential for managing the various complications associated with leukopenia. The three components of myelosuppression management are: prevention of infection, frequent patient assessment for the early detection of infection, and aggressive management when such infection arises. The oncology nurse minimizes patient- and environment-related sources of infection and is aware that detection is complicated by the lack or diminution of signs and symptoms in a leukopenic patient. Infections that arise are managed in different ways, depending on the pathogen and on available therapy. In addition to conventional antimicrobial therapy, newer therapeutic modalities, such as colony-stimulating factors, may hold promise for the treatment of leukopenic patients. The nurse is responsible for many aspects of the care for these patients.