This study appears to represent the first serotyping study of 24 isolates of Avibacterium paragallinarum obtained from different regions of Peru during 1998-2008. All isolates were characterized as beta-nicotinamide adenine dinucleotide dependent. According to the Page scheme, modified by Blackall, it was found that eight isolates were classified as serogroup A, seven isolates as serogroup B, and five isolates as serogroup C, while four isolates could not be serotyped. Further serotyping, following the same scheme but using rabbit antiserum raised against Argentinean strains of the three serogroups, allowed allocation of these four unclassified isolates to serogroup B. These results suggest that some of the Peruvian B isolates appear to be similar to the previously described variant B isolates from Argentina. Therefore, inactivated vaccines used in Peru should include the three recognized serogroups (A, B, and C), with the addition of at least one of these variant B isolates. Cross-protection trials are needed to compare the protection conferred by vaccines containing traditional B serovar strains to the protection by experimental vaccines containing variant B serovar isolates from Peru.