Variations in the nucleotide sequence of 3 C proteinase of coxsackievirus A 24 variant (CA 24 v) were analyzed to define the route of transmission and spread of the virus which was introduced to Japan on three separate occasions, 1985-86, 1988, and 1989. The nucleotide sequences of isolates from the same year's outbreak in Japan were identical or closely related, while the isolates from different outbreaks were less closely related to one another than to those from other countries in the same year. All Japanese isolates from Okinawa and other prefectures in 1985 and 1986 were closely related to the Taiwan strains in those same years, indicating common-source outbreaks. Two 1988 isolates from Chiba Prefecture, Japan, were closely related to those from Singapore in 1987, China in 1988 and Hong Kong in 1988. All seven Japanese isolates from Chiba Prefecture in 1989 comprised a group together with the Taiwan and Singapore strains in 1988. The results indicate that CA 24 v was introduced into Japan on each occasion from the outside. Furthermore, in contrast to the explosive epidemics in Okinawa Prefecture in 1985 and 1986, the virus which was repeatedly introduced to other areas in Japan did not circulate endemically, and disappeared within a short time.