The rapid spread of the high-yielding varieties of rice in Asia has been associated with outbreaks of several virus diseases. Insect transmission studies were mainly carried out during the 1970s. The five- year Research Project on Virus Diseases of Rice and Legumes in the Tropics which was initiated in 1978 by the Tropical Agriculture Research Center in collaboration with the Insitute for Plant Virus Research and others, involved a sub-center under the Department of Agriculture, Thailand. TARC provided a set of equipment including an electron microscope, and Japanese long-term visiting researchers were dispached to work in collaboration with the Thai researchers. Several Japanese short-term visiting researchers carried out surveys overseas and brought back virus materials to Japan to undertake more precise studies using the facilities in Tsukuba. The properties of the viruses, distribution, mode of transmission by vectors, epidemiology, and serology, etc. were studied. Serological diagnosis of the diseases were developed and is being used at IRRI at present. Rice ragged stunt, rice tungro, rice gall dwarf, rice transitory yellowing, and rice grassy stunt diseases are important and the etiology and properties of the causal viruses were studied. Rice gall dwarf virus was identified and studied in some detail before the epidemic of 1983. Cell lines of insect vectors have been established.