SummaryOrgan cultures of mouse trachea were infected with some indigenous mouse viruses. Mengovirus and reovirus type 3 grew to high titer; inocula of, respectively, 102 and 10 a TCID50 were required to initiate infection. Organ cultures supported also the growth of mouse hepatitis viruses, MI-IV-3 and MHV-S, though to a lesser extent. Viral production was noted for periods of as long as two weeks. None of the viruses had a noticeable effect on the ciliary activity or acquired such capacity on serial passage in organ cultures.