Abstract
A microneutralization fluorescent-antibody (MFA) test was effective in determining the level of antibodies to avian infectious bronchitis virus. A comparison of the MFA test with the cytopathic effect microneutralization (MNT) test and 50% plaque reduction (PR) test resulted in positive correlations that were significant (P less than 0.001). The PR test was more sensitive than either the MFA or the MNT test, but there was no significant difference between the sensitivities of the MFA and MNT tests. The MFA test has advantages over the PR test in the capacity to test large numbers of sera in a shorter period of time. The MFA test also can be completed in one-half the time required for the MNT test.