Previous reports have indicated that patients with severe acute respiratory syndrome (SARS)-associated coronavirus infection could develop atypical pneumonia with fulminant pulmonary edema. However, the target cells of SARS viral infection have not been characterized in detail. We report the pathologic findings of the lung in 3 cases of SARS. Chest radiographs at 2 to 3 weeks of infection revealed an atypical pneumonia with pulmonary consolidation, a clinical characteristic of SARS infection. The presence of the SARS virus was determined by nested reverse transcription-polymerase chain reaction (RT-PCR), and the infected cells were identified by in situ hybridization in open-lung biopsy and postmortem necropsy specimens. Expression of SARS virus-encoded RNA was detected in all 3 cases by RT-PCR, and the SARS viral signal was localized in pneumocytes by using in situ hybridization.