AIM: To summarize clinical features of probable severe acute respiratory syndrome (SARS) in Beijing. METHODS: Retrospective cases involving 801 patients admitted to hospitals in Beijing between March and June 2003, with a diagnosis of probable SARS, moderate type. The series of clinical manifestation, laboratory and radiograph data obtained from 801 cases were analyzed. RESULTS: One to three days after the onset of SARS, the major clinical symptoms were fever (in 88.14% of patients), fatigue, headache, myalgia, arthralgia (25-36%), etc. The counts of WBC (in 22.56% of patients) lymphocyte (70.25%) and CD(3), CD(4), CD(8) positive T cells (70%) decreased. From 4-7 d, the unspecific symptoms became weak; however, the rates of low respiratory tract symptoms, such as cough (24.18%), sputum production (14.26%), chest distress (21.04%) and shortness of breath (9.23%) increased, so did the abnormal rates on chest radiograph or CT. The low counts of WBC, lymphocyte and CD3, CD4, CD8 positive T cells touched bottom. From 8 to 16 d, the patients presented progressive cough (29.96%), sputum production (13.09%), chest distress (29.96%) and shortness of breath (35.34%). All patients had infiltrates on chest radiograph or CT, some even with multi-infiltrates. Two weeks later, patients' respiratory symptoms started to alleviate, the infiltrates on the lung began to absorb gradually, the counts of WBC, lymphocyte and CD(3), CD(4), CD(8) positive T cells were restored to normality. CONCLUSION: The data reported here provide evidence that the course of SARS could be divided into four stages, namely the initial stage, progressive stage, fastigium and convalescent stage. (c) 2005 The WJG Press and Elsevier Inc. All rights reserved.