Between January 1976 and March 1982, 28 episodes of pneumonia occurred in 26 renal transplant patients. The overall mortality rate was 46%. Of the 16 patients with nosocomial pneumonia 9 (56%) died, whereas of the 12 patients with community-acquired pneumonia 4 (33%) died. In all 9 cases of unknown cause the response to empiric treatment was prompt, whereas in 4 of the 10 cases of monomicrobial pneumonia and 8 of the 9 cases of polymicrobial pneumonia the patient died. Cytomegalovirus was the sole cause of the pneumonia in two patients and a contributing cause, along with aerobic gram-negative bacteria, in another five, four of whom also had a fungal infection. Two patients, both of whom survived, had nosocomial Legionnaires' disease.