The growth of ten strains of avian infectious bronchitis virus (IBV) in several cultured cells was examined. The cultured cells used were chick kidney (CK), chick embryo (CE), HeLa and BHK-21 cells. The results obtained can be summarized as follows. 1. All the strains showed similar growth curves in CK cells. Progeny viruses appeared in the culture medium 4 to 6 hours after inoculation and peak virus titers of 10(6.5)--10(8.5) TCID50 per 0.1 ml were obtained after 36 hours. A cytopathogenic effect (CPE) was detected within 24 hours. No distinct CPE and low multiplicities were observed on culturing at 30 degrees C. 2. All strains replicated in CE cells, although only small amounts of virus were produced. No CPE was observed. 3. Only Beaudette-42 and Holte strains grew in BHK-21 cells. 4. No IBV strains grew in HeLa cells.