Immunogenetic studies showed that Behçet's disease has a primary association with HLA-B antigen (HLA-BW51) and the same association throughout the world, whereas, Vogt-Koyanagi-Harada's disease (VKH) is primarily associated with supertypic HLA-DR antigen (MT3), an HLA-D-linked B cell alloantigen in Japanese. Immunological investigation showed that the serum levels of gamma-interferon (IFN-gamma) were significantly increased in both Behçet's disease and VKH, IFN-gamma showed a significant decrease in the ocular exacerbation stage in Behçet's disease. The highest IFN titre was observed 1 to 2 months after the onset of the disease in VKH.