A chemiluminescence immunoassay (CLIA) for detection of SARS-CoV (severe acute respiratory syndrome-associated coronavirus) nucleocapsid (N) protein was established.The culture supernatants of 34 strains of Cov and 49 sera of SARS patients were detected for SARS-CoV N protein using CLIA.The culture supernatants of all 6 SARS strains were pos. for SARS-CoV N protein by CLIA, while none of 11 other viruses were pos. for the protein.The min. detection level of the CLIA was 6.3 PFU/mL of SARS-CoV.The pos. rate of SARS-CoV N protein was 100% in SARS patients 6-10 days after onset of the disease.The CLIA was sensitive and specific for detection of SARS-CoV N protein, and might be used for earlier diagnosis of SARS-CoV infection.