Two serological tests, the agar gel precipitation (AGP) test and the enzyme-linked immunosorbent assay (ELISA), were used to measure antibodies against infectious bronchitis virus (IBV). A total of 259 pooled chicken sera (5 birds/sample) were examined by both tests. 212 (81.9%) sera were positive in ELISA, while only 33 (12.7%) sera had precipitating antibod ies and 47 (18.1%) sera were negative in both tests. It was demonstratd that, based on the higher sensitivity, the ELISA test is more suitable than AGP to measure IBV antibodies.