Recent studies have revealed the important role of streptococci in the etiology of Behçet's disease. Among patients with Behçet's disease, there is a high incidence of a history of streptococcal infections. Certain antigens of streptococci induced not only cutaneous, delayed-type hypersensitivity, but also systemic attacks of Behçet's disease when skin tests were performed. Neutrophil-activating lymphokines are produced when streptococcal antigen reacted with lymphocytes from patients with Behçet's disease. The first international diagnostic criteria for Behçet's disease were prepared by multicenter studies and published recently. With recent progress in diagnostic imaging techniques, magnetic resonance imaging and position emission tomography are particularly important for the diagnosis of neuro-Behçet's disease. In Japan, cyclosporin was also proved to be effective for eye lesions of Behçet's disease in a double-blind clinical trial comparing this drug with colchicine.