A differentiated tissue model was used to study the course of cytomegalovirus infection in respiratory epithelium in vitro. Mouse tracheal rings in organ culture were infected with murine cytomegalovirus. Infectious virus in the medium reached average titers of 10(5.5) plaque-forming units/ml by day 17. Infected epithelial cells on the rings contained viral antigen as demonstrated by immunofluorescence staining; light microscopy of these cells revealed enlarged nuclei, cytoplasmic vacuolization, and nuclear and cytoplasmic inclusions characteristic of infection with cytomegalo-virus. Development of viral particles, as visualized by electron microscopy, was similar to that observed in other types of cells.