Hyperreactivity of the skin to intracutaneous injection or needle prick (the pathergy test) is a unique feature of Behçet's disease. This phenomenon has been demonstrated to be highly sensitive and even specific in patients with Behçet's disease from Turkey, Japan, and Israel. A lack of positive reaction to this test has been reported in British and American patients. To evaluate the specificity of the pathergy test's results in Israeli patients with Behçet's disease, we compared their prevalence in these patients to that in a group of patients with other diseases associated with vasculitis. Forty-six Jewish and Arab Israeli patients with Behçet's disease, during a period of peak activity of their disease, and forty-six patients with other diseases associated with vasculitis, were studied for the hyperreactivity phenomenon. A positive reaction was observed in forty-five of forty-six patients with Behçet's disease, while the test gave negative results in all those with other diseases. Our study indicates, therefore, that the results of the pathergy test are highly sensitive and specific for Behçet's disease in Israeli patients.