Influenza HINI viruses isolated in Japan in 1978–1979 were compared with A/USSR/ 92/77 and HINI viruses isolated in North and South America in 1978 by oligonucleotide mapping of viral RNA. At least four types of HINI viruses, distinguished by oligonucleotide pattern, were involved in influenza outbreaks during 1978–1979 in Japan. The first type was prevalent throughout the country from January to March 1978. The second and third types caused sporadic outbreaks during the 1978–1979 winter. The second type was closely related to an HINI strain of 1953, A/Omachi/1I53; the third type appeared to be reintroduced from outside of Japan. The fourth type was prevalent from January 1979 and persisted to September 1979. Its origin was a virus closely related to AlCalifornia/45/78 virus, which appeared in the United States in late 1978. The oligonucleotide pattern of A/California/45/78 viral RNA was markedly different from that of other 1977–1978 HINI viruses; the major change occurred in the polymerase and nucleoprotein genes.