We used the whole lung section technique to review the macroscopic pathology in 12 patients who died with Legionnaires' disease. None of these patients had been treated with erythromycin. Consolidation was evenly distributed throughout all lobes without a consistent segmental distribution. The smallest lesions were around bronchioles or bounded by lobular septa. In most cases there was confluent involvement of multiple lobules. Extensive consolidation made distinction between a lobar and confluent lobular distribution difficult. Abscesses were present in two cases and nodular infiltrates in two others. In five additional patients, Legionnaires' disease had been treated with erythromycin. Four had a clinical response to treatment, and the fifth had diffuse staphylococcal pneumonia as the predominant lesion. Because the lungs of all five patients contained bacteria other than the Legionnaires' disease bacterium at the time of autopsy, it was difficult to ascertain the role of Legionnaires' disease bacterium in the pathology.