For evaluation of specificity and sensitivity of flowcytometric determination of HLA-B27 antigen, we determined the HLA-B27 on lymphocytes using HLA-B27 monoclonal antibody by flow cytometer. Data were compared to those by conventional Terasaki microlymphocytoxicity test and DNA genotyping Polymerase Chain Reaction (PCR) method. One hundred and ninety four patients with various forms of arthritis were included in this study. Forty one of them were HLA-B27 positive, confirmed by three methods concomitantly with complete accordance. None of serological B27 negative, B7 CREG positive cells were found to be flowcytometric fluorescence positive. Furthermore, there was no significant difference of B27 intensity between different B27 DNA subtypes, nor was there any difference between primary ankylosing spondylitis (AS) and other secondary spondylitis patients as measured by mean channel of fluorescence. It is suggested that flowcytometric measurement of HLA-B27 antigen is a rapid and reliable method for HLA-B27 determination.