Listeriosis in a chicken from a small farm was diagnosed by the peroxidase-antiperoxidase (PAP) method. The animal had diffuse myocarditis and necrotic foci in the liver and in the spleen. PAP technique performed on formalin-fixed tissues confirmed the presumptive diagnosis. Serological and microbiological studies were also done. It is concluded that PAP method is useful for the diagnosis of avian listeriosis allowing retrospective studies with formalin-fixed, paraffin-embedded tissues, avoiding cumbersome microbiological culture. © 1988, Taylor & Francis Group, LLC. All rights reserved.