The entry route of viruses into the inner ear is still controversial. Guinea pig cytomegalovirus (CMV) has been used to create an animal model of systemic infection as well as labyrinthitis. In this study, seronegative guinea pigs were administered intracardiac inoculations of varying doses of guinea pig CMV. After three or eight days, the animals were killed and necropsy specimens examined for viral antigen. In the specimens examined three days after inoculation, no label was seen in the cochlea. However, label was found in the spleen with doses of 100 microL, and also in the liver in animals inoculated with 300 microL of virus. After eight days, an animal that received 200 microL of the virus showed labeling in the modiolar blood vessels and perivascular infiltrates. Two of the four animals that received 300 microL of the virus showed labeling in spiral ganglion cells. None of the animals showed viral antigen within the stria vascularis, nor were there signs of acute labyrinthitis. At eight days, animals inoculated with greater than 100 microL of virus showed labeled cells in multiple organs. These data suggest that the entry route of guinea pig cytomegalovirus into the inner ear might involve viremic spread to modiolar blood vessels and subsequent spread to spiral ganglion cells.