Forty-six episodes of pulmonary infection occurred in 41 patients during a seven year period in which 187 renal transplants were performed in 168 patients. Thirty-seven episodes followed 152 cadaveric transplants (24.39%), and four episodes followed 35 living related donor transplants (11.4%). Five patients had two episodes of pulmonary infection. Twenty-four patients recovered, and 17 died (41.5%). Pulmonary infections appeared from two days to three years after transplantation, but predominated in the first four months (32/46). They were caused primarily by bacterial agents (74%) with protozoa, fungi, and viruses appearing less frequently. In 35 episodes, a single etiologic agent was found, but 11 were caused by two or more agents. When compared with noninfected recipients, there was no significant difference with regard to number of rejection crises, maintenance prednisone dosage, or blood glucose. However, subnormal renal function was significantly associated with the development of infection. Azathioprine dosages were actually higher for the noninfected patients, reflecting a tendency to lower the dose of azathioprine in the presence of decreased renal function. Fever was the most common presenting symptom. Transtracheal aspiration with Gram stain and direct sensitivity plating routinely provided early and accurate identification of the organism and a guide for therapy in bacterial infections. Pulmonary infection in renal transplant recipients is associated with a high mortality rate. Early diagnosis and specific treatment are essential to successful management.