The primary target of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) is epithelial cells in the respiratory and intestinal tract. The cellular receptor for SARS-CoV, angiotensin-converting enzyme 2 (ACE2), has been shown to be localized on the apical plasma membrane of polarized respiratory epithelial cells and to mediate infection from the apical side of these cells. Here, these results were confirmed and extended by including a colon carcinoma cell line (Caco-2), a lung carcinoma cell line (Calu-3) and Vero E6 cells in our analysis. All three cell types expressed human ACE2 on the apical membrane domain and were infected via this route, as determined with vesicular stomatitis virus pseudotypes containing the S protein of SARS-CoV. In a histological analysis of the respiratory tract, ACE2 was detected in the trachea, main bronchus and alveoli, and occasionally also in the small bronchi. These data will help us to understand the pathogenesis of SARS-CoV infection.