On the general surgical service, five postoperative patients died during a six-month period of pulmonary infections. All developed pneumonias caused by gram-negative bacteria that were resistant to the antibiotics employed immediately after surgery. In all cases, the antibiotics provided broad-spectrum coverage and were not directed initially against any specific bacteria. The authors caution against the use of prophylactic antibiotics in postoperative patients, particularly in those predisposed to develop pulmonary infections.