ABSTRACTCytomegalovirus is the most frequently recognized cause of congenital viral infection and of viral induced congenital hearing loss. Histopathologic reports on temporal bones from nine congenitally infected infants have most often demonstrated an endolabyrinthitis.The guinea pig and its specific cytomegaloviruses have been studied extensively as a model of transplacentally acquired infection. However, to date no investigation has been performed on the inner ear of such congenitally infected animals. To determine if a congenital viral labyrinthitis occurs in these guinea pigs, a study was conducted in which pregnant Hartley and Strain 2 guinea pigs were injected intraperitoneally with virulent salivary gland passaged cytomegalovirus during the first, second, or third trimester. Various durations of gestation up to delivery were permitted and selected organs from the products were then studied with routine histologic and immunocytochemical methods and cell cultures to verify the presence of transplacental infection. The temporal bones were studied with routine histopathology as well as immunocytochemical methods to detect cytomegalovirus antigen. Over 190 products of conception studied in this fashion revealed no evidence of teratogenesis or labyrinthine infection. It is not clear why in the presence of viremia, which resulted in cytomegalovirus infection of multiple organs, the inner ears of these animals were apparently spared.