The immunogenetic mechanisms of various ocular diseases were investigated utilizing recently developed molecular biological and molecular genetic techniques. It was revealed that HLA-B 51 was closely associated with Behçet's disease. Investigation of genetic polymorphism of TNF-beta (tumor necrosis factor-beta) showed that 95% of Behçet's disease patients had the 10.5 kbp Nco I fragment. It was therefore concluded that the gene of susceptibility to Behçet's disease is located between HLA-B and TNF-beta loci on the short arm of chromosome 6. Similar studies of HLA-DNA typing in Harada's disease frequently seen in Japan showed that frequencies of HLA-DRB1 * 0405, HLA-DQA1 * 0301 and HLA-DQB1 * 0401 were significantly increased in patients compared with normal controls. These data suggested that those who have serine at position 57 of HLA-DR, glutamic acid at position 70 and aspertic acid at position 71 of HLA-DQ respond to certain unknown agents significantly more than those without them, thus leading to the development of Harada's disease. The same HLA association was observed between Harada's disease and sympathetic ophthalmia, and the immunogenetic mechanism was thought to be similar in both diseases. Recent immunogenetic and molecular genetic investigations on various ocular diseases have shed new light not only on the genetic individual susceptibility and biased racial differences, but also on the diagnosis of the ocular diseases, reclassification of disease entities according to HLA associations, and judgement of disease prognosis. Further progress of molecular medicine may make it possible to treat various intractable ocular diseases by gene therapy in the near future.