Abstract: The present invention provides methods for locating critical portions or sites on the spike protein (S protein) of SARS-associated coronavirus (SARS-CoV) responsible for the viral infection that causes Severe Acute Respiratory Syndrome (SARS). The present invention also provides new synthetic peptides targeting such critical portions or sites of the S protein of SARS-CoV for preventing or treating of SARS-CoV infection in a subject. The present invention further provides methods of testing antiviral activity exerted by antiviral agents using real-time quantitative PCR.