Two inbred lines of White Leghorn chickens, line C which are highly resistant to infection with avian infectious bronchitis virus (IBV), and line 151, which are highly susceptible, were challenged at 11 days of age with IBV Massachusetts-41 (M41) strain. Line 151 chickens showed more severe respiratory signs than line C and although similar amounts of virus were recovered from the tracheas of both lines for the first four days after inoculation, overall more virus was recovered from the respiratory tract organs and from kidneys of line 151 chicks. There was however, no difference in the rate of virus production or in the amount produced by explants of tissues from each line following inoculation with IBV in vitro. When tracheal ciliary movement of lines C and 151 chickens was examined following inoculation with M41. ciliostasis was observed earlier in line 151 than in line C and lasted for a longer time.