A hemagglutinating virus was reported to be frequently isolated from laboratory mice by us in Japan (Fukumi et al, 1954) . This virus was later proposed to be called HVM (hemagglutinating virus of mice) by us, but as several independent names were adopted by several groups of investigators and more confusion was apt to occur, a committee was established by the Society of Japanese Virologists to control such confusion. This committee finally agreed to propose the name HVJ (hemagglutinating virus of Japan) for the virus in question. This virus is however, widely called Sendai virus in countries outside of Japan since Jensenet al.'s publication (Jensenet al., 1956), where they proposed to call it as influenza virus D. Now it seems fairly well accepted that the virus belongs toMyxovirus parainfluenzaetype 1, though there is still some reservation (Fukumi and Nishikawa, 1961) .
As this virus has been considerably widely distributed among laboratory mice, it has often caused disturbances in experiments in which intranasal inoculations of laboratory mice are employed, especially experiments dealing with mouse passages of influenza and some other viruses. This situation prompted us to conduct experiments concerned with epidemiology and some other features of Sendai virus infections in laboratory mice.
