In order to understand the role of monocytes and macrophages (M) in the pathogenesis of SARS, we detect pathological changes, cell apoptosis and expression levels of CD68, Mac387, CD25, ACE2 and S protein in the specimens of lungs, spleen and lymph nodes. Plenty of infiltrating M could be seen in a number of tissues including the alveolus cavity, the lymphatic sinus in lymph nodes and the splenic pulp. Expression of ACE2 and S protein was detected in the M of lungs, spleen and lymph nodes. Compared with normal tissues, the number of apoptotic cells was increased significantly in the M of lungs, spleen and lymph nodes in SARS patients. Our previous hypothetic model for the immunopathogenesis of SARS has been further confirmed by the present observation. It is, therefore, of clinical significance to find a way to block the pathway of M -mediated activation of pro-inflammatory cytokines (PICs).