A trypsin-induced haemagglutination inhibition (THI) assay was standardized to achieve a quantification of haemagglutinating-inhibiting antibodies against infectious bronchitis virus (IBV) in the sera of chickens vaccinated with different types of commercial imported IBV vaccines. A total of forty four IBV vaccines representing as twenty two live vaccines containing either classical or variant strains and twenty two inactivated vaccines were examined among (THI) assay using trypsin treated classical IB antigen. In a trial for studying the correlation between the results of THI and the other serological tests (ELISA and serum neutralization test "SNT"). The former tests were performed on the same serum samples used in (THI) test. The results showed that the calculated mean HI titers for different examined serum samples ranged between 7.7 log₂ to 7.9 log₂, against live IB variants vaccines (CR88 and 4/91 respectively), 8.7 log₂ to 9.2 log₂ against classical type (Ma5, H120) vaccines, 9.1 log2 (H120+D274) and 6.8 log₂ against inactivated vaccines. It was observed that quantification of antibodies in sera of chickens against infectious bronchitis virus by HI test had correlation with those obtained by either ELISA or SNT tests.