An ELISA test for detection of influenza A virus type-specific antibodies in chicken and turkey sera is described. Antigen was prepared from infected allantoic fluids using an H7N1 virus. Virus particles were disrupted using sodium deoxycholate to release internal antigens and tests were standardised by testing batches of sera from influenza-free birds. A negative antigen was included in the test and was shown to be effective in eliminating the non-specific increase in absorbance values observed with influenza-negative sera from older birds. Sensitivity and group-specificity were demonstrated by infection of chickens and turkeys with influenza subtypes unrelated to the H7N1 virus from which the antigen was prepared, so that only type A specific responses were being detected. The sensitivity was equivalent to the haemagglutination-inhibition test. Antisera to all 13 haemagglutinin subtypes, prepared in chickens, were strongly positive, again highlighting the group reactivity of the test and demonstrating its suitability as a screening test.