Hantavirus-induced acute viral infection of the inner ear of guinea pigs is reported. Guinea pigs were inoculated directly into the inner ear through the round window, or intraperitoneally with hantavirus (B-1 strain), and the cochlea was examined using an immunohistochemical technique for the localization of viral antigens. Virus-specific antigens were detected prominently in the stria vascularis and to a lesser degree in other inner ear structures of the infected guinea pigs. The morphological changes in the inner ear structures of these guinea pigs were observed. Virus was isolated from the blood of some infected guinea pigs. These data suggest that hantavirus can infect the inner ear of the guinea pig via viremia. The effect of immunosuppression by ciclosporin A or cyclophos-phamide is discussed.