The clinical presentation and radiographic progression of Legionnaires' disease is described in 10 renal transplant patients, the majority undergoing treatment for rejection. Presentation with pleuritic chest pain, fever, hypoxia, and hemoptysis was typical and in some cases led to confusion with pulmonary embolism. The radiographic appearance was that of rapidly progressive, dense, sublobar consolidation, occasionally showing patchy spread to other areas and usually accompanied by pleural effusion. Cavitation occurred in seven of 10 patients.