Skin hypersensitivity to needle puncture (pathergy test) together with a positive HLA B5 antigen has been reported as a diagnostic test for Behçet's syndrome (BS) in Turkish patients. We have studied the pathergy test by 2 methods in 7 healthy volunteers who have the HLA B5(Bw 51 split) antigen and 19 patients with BS. The test was negative in all the normal volunteers and only one of the 19 patients with BS had a positive test by one of the 2 methods. Cluster analysis of our patients and those reported from Turkey showed no difference in their clinical features. The positivity of the pathergy test, and hence its diagnostic usefulness, seem to differ between Britain and Turkey, and we conclude that this difference is not related to the possession of the HLA B5 (Bw 51 split) antigen.