Since mid February 2003, there have been reports of atypical pneumonias originating in China which have subsequently been termed the Severe Acute Respiratory Syndrome (SARS). SARS has subsequently spread to multiple countries including the United States, and is accompanied by a higher than anticipated morbidity and mortality. Because of world travel and the apparent easy transmissibility of this disease reported in other nations, the number of patients with SARS may continue to rise. The primary purpose of this protocol is to evaluate and treat persons with SARS. Other goals will be to characterize the clinical course of SARS by also evaluating close contacts of people with SARS, as well as those that have recovered from SARS. Additional goals of the protocol are to elucidate the pathophysiology of SARS, characterize the immune response during SARS, and evaluate diagnostic tests for the rapid identification of SARS in clinical specimens. Further knowledge about SARS may lead to effective forms of therapy and improve mortality from this disease.