Several strains of wild-type influenza A virus were studied in the ferret tracheal organ culture system. Ciliary activity and viral replication were measured. Ciliary activity was reduced more rapidly by A/Hong Kong/45/68 (H3N2) (A/HK) and A/Victoria/3/75 (H3N2) (A/Vic) than by A/New Jersey/8/76 (Hsw1Nl) (A/NJ), A/Scotland/840/74 (H3N2) (A/Scot), or A/USSR/90/77 (H1N1) (A/USSR). A/HK, A/Vic, and A/Scot produced titers of virus higher than A/USSR or A/NJ during the first three days after infection. Differences in effects of the five viruses on cilia were not related to history of egg passage. The two strains that destroyed ciliary activity rapidly had caused excess mortality in the United States, whereas the three that destroyed ciliary activity more slowly had not. A relationship may exist between the properties contributing to virulence in humans and the destruction of ciliary activity in vitro in this culture system.