Tissue typing can help in the diagnosis of the seronegative arthropathy ankylosing spondylitis. Using an automatic sample preparation system and flow cytometry (FACSPrepiFACScan) we have developed a test for HLA-B27 screening using whole blood which is both rapid, reproducible, and permits simultaneous screening of large numbers of samples. We have used both indirect (248 cases) and direct (126 cases) monoclonal antibody staining techniques. Results were assessed using median channel shift (CS) from the negative control and relative fluorescence intensity. There is known cross-reactivity between HLA-B27 and HLA-B7 with the monoclonal antibody (MoAb) HLA-ABC-m3. Using this antibody and indirect staining, HLA-B7 samples had a significantly lower CS value than HLA-827 samples. In 60% of these cases there was a clear distinction between HLA-B27 and HLA-B7. All HLA-B27 and HLA-B7 negative samples had a CS of 0 ( P < 0.001). Using direct dual staining with CD3 and HLA-B27, all HLA-B27 and HLA-B7 negative samples had a low CS value (15 maximum), HLA-B7 samples had an intermediate CS value samples had the highest CS values (70 upward). This system permits large scale rapid negative screening of samples with the elimination of over 60% as negatives (CS < 15). Limitations as a definitive test for HLA-B27 are due to MoAb cross-reactivity with HLA-B7 which necessitates other confirmatory techniques. The substitution of the HLA-ABC-m3 with the recently available HLA-B27 specific MoAb FD705 would substantially increase the value of this technique for routine HLA-B27 typing. o 1994 Wiley-Liss, tnc.