Patients with lymphoid malignancies such as chronic lymphocytic leukemia, particularly those who receive the newer purine analogs, are at increased risk for infectious morbidity and mortality. Defects in cell-mediated immunity appear to be a major predisposing factor in these patients. An expanding spectrum of pathogens associated with lymphocytopenia and depletion of CD4 has been described in the setting of therapy with purine analogs. During the past 2 years new knowledge about the immunosuppression related to that treatment has continued to accumulate.