Gram-negative bacillary pneumonia is common in all groups of iatrogenically immunosuppressed patients. Mortalities are directly proportional to the degree of neutropenia. Those at particular risk for gram-negative pneumonia are neutropenic patients, patients residing in the hospital setting for prolonged periods, and patients in postoperative periods (eg, organ transplant recipients). The most frequent pathogenesis for pneumonia appears to be airway colonization with gram-negative bacilli, followed by lowe respiratory tract infection. Thus, attention to infection control measures and surveillance culture data is important. Because sputum production is scant or absent, and blood cultures positive in only 30% to 40% of patients, it is often difficult to identify specific etiologic agents. If bacterial pneumonia is suspected in the immunocompromised host, empiric antibiotic coverage should include drugs active against all common aerobic gram-negative bacilli (including P aeruginosa), plus S aureus. Most advocate a beta-lactam plus aminoglycoside combination. Adjunctive treatment with granulocyte transfusions should be reserved for patients not responding to traditional regimens. Immune therapy or prophylaxis has not been fully evaluated for the immunocompromised patient population.