Records of 133 infections occurring in 73 of 125 patients with late-stage non-Hodgkin's lymphoma on intensive chemotherapy programs for a median of 23 months were reviewed. Granulocytopenia, usually related to chemotherapy, was the major predisposing factor, association with 51% of infections. The incidence of infection in chemotherapy courses associated with less than 500 granulocytes/microL was higher than those with 500 or more granulocytes/microL (p = 0.0004). Splenectomized patients tended to have a higher incidence of chemotherapy courses with an infection (p = 0.06); marrow involvement was not a significant predisposing factor to infection. The commonest sites of infection were lung, skin, and alimentary canal. Gram-negative organisms and Staphylococcus aureus caused 83% of documented infections; Pseudomonas aeruginosa was the major cause of pneumonia and bacteremia; and herpes zoster and fungi each caused only 3% of infections. Other infections associated with impaired cellular or humoral immunity were uncommon. Poor prognosis was associated with infections in granulocytopenic patients with stable or falling granulocyte counts, infection at multiple sites, and bacteremia, especially polymicrobial bacteremia.