Infectious complications were studied in 14 patients who received heart-lung transplants at Stanford University Medical Center from March 1981 to November 1983. Twenty-nine infections occurred in 12 patients: 18 bacterial, nine viral, and two fungal. Sixteen (89 percent) of the bacterial infections occurred in the lung. Because of frequent colonization of the lower respiratory tract, the specificity of transtracheal aspiration and bronchoscopy was low. Empiric broad-spectrum antibiotic therapy was usually successful, and no patient died of bacterial infection. Cytomegalovirus infection occurred in six and herpes simplex virus infection in three patients. Two patients had invasive candidiasis at postmortem examination. This series emphasizes the importance of infection, particularly of the lung, in causing morbidity and mortality in heart-lung transplant recipients.