Objective To analyse the number of dendritic cells and macrophages and the size of macrophages in the spleen of SARS patients so as to provide evident for the study of pathology and pathogenesis of SARS. Methods Immunohistochemical method with four specific antibodies(S100, CD68, HLA-DR, CD83) were used to detect the dendritic cells and macrophages in the spleens of six dead patients of SARS and six accidental deaths as the controls, The number or the size of these positive cells was analysed with image analysis system. Results In the spleens of SARS patients, the number of S100+ dendritic cells in the white pulp was reduced by 80.4% on average, and even disappeard. The number of CD68+ macrophages in the red pulp was reduced by 39.48% in SARS spleens, and the average size of individual macrophages was increased by 2.21 times. HLA-DR\++ antigen presenting cells (APC) reduced remarkably in the SARS spleen white pulp. CD83+ mature dendritic cells did not exist in either SARS spleens or the control spleens.Conclusion The function of antigen presentation had been damaged severely, which supports that SARS should be categorized as a viral immune deficiency disease. SARS virus doesn’t induce the maturation of DC.The increase in the size of macrophages indicated that they were in an activated state and may play a role in the pathogenesis of SARS.