Cavitation is an unusual manifestation of legionnaires' pneumonia. Mortality rates range from 24 to 58 percent with effective therapy. Antibiotic therapy is not standardized and is largely based on anecdotal reports. This report has described nosocomially acquired cavitary legionnaires' pneumonia in five renal transplant recipients. The diagnosis was made by seroconversion and immunofluorescent staining of lung tissue or transtracheal aspirates. Frequently seen associated symptoms were not present. All patients were successfully treated with 2 to 4 g of erythromycin for at least 4 weeks.