People 18 years of age and older with probable or suspected SARS may be eligible for this study. Close contacts of patients with SARS, patients who recovered from SARS, and NIH health care workers involved in the care of patients will also be enrolled. Patients with SARS who require hospitalization will be admitted to the NIH Clinical Center. Because SARS spreads easily, hospitalized patients will be in a room by themselves and will not be allowed any visitors. They will not leave their room except for tests, such as x-rays.