AIMS: Natural killer T (NKT) cells, T lymphocytes expressing both T cell and NK cell markers, are suggested to be involved in autoimmune diseases. To examine the relation between the pathogenesis of uveitis and CD56+ T cells, which are thought to be a type of human NKT cells, we investigated peripheral CD56+ T cells in uveitis patients. METHODS: 41 uveitis patients (Behçet's disease (BD), 14; sarcoidosis (SAR), eight; Vogt-Koyanagi-Harada disease (VKH), five; idiopathic uveitis (IU), nine; and others, five) and 19 healthy controls participated in this study. Cell surface antigens of lymphocytes were analysed by use of monoclonal antibodies and flow cytometry. RESULTS: The proportion of CD56+ T cells in patients with BD was higher than in controls and in patients with SAR, VKH, IU, and others. CONCLUSION: Increased peripheral CD56+ T cells might be relevant to the pathogenesis of uveitis in BD, and increase of peripheral CD56+ T cells may be one of the laboratory findings to suggest that uveitis originates from BD.