HLA-B27 has been demonstrated to be strongly associated with ankylosing spondylitis (AS), a chronic inflammatory disease affecting the axial muscoskeletal system. Routine clinical tests detecting HLA-B27 include cytotoxicity, immunofluorescent, and flowcytometry-based assays, among which the later showed flowcytometry assays are the best advantages of specificity and rapidity in performance. In recent years, however, application of PCR-based DNA typing resulted in a more reliable assay for HLA-B27 detection. In the present study, the authors detected HLA-B27 in blood samples of patients suspected to have AS, by both flowcytometry-based and PCR-SSP-based assays, in order to assess the value of each method in HLA-B27 detection. The results showed that: - Flowcytometry-based assay can detect cell surface HLA-B27 expression when positive and negative events got a clear cut over the cut-off level (the real positive and negative results). - PCR-SSP-based assay is of much help in detecting HLA-B27 encoding gene when flowcytometry based assay was unable to determine the expression of HLA-B27 (the undetermined results).