Pigeon herpes encephalomyelitis virus (PHEV) was compared with seven avian herpesviruses for antigenic relatedness using monospecific antisera and the indirect fluorescent-antibody (IFA), agar-gel-immunodiffusion, and serum-neutralization tests. No antigenic relationship was detected between PHEV and Marek's disease virus, turkey herpesvirus, infectious laryngotracheitis virus, and duck enteritis virus. A common precipitating antigen was detected between the PHEV and pigeon herpesvirus (PHV), owl herpesvirus (OHV), and falcon herpesvirus (FHV). These four viruses also cross-reacted in the IFA test. Weak neutralizing activity was detected only between PHV antiserum and PHEV. These results suggest that the PHEV should be classified as a herpesvirus related to, but distinct from, the PHV-OHV-FHV group of viruses with which it shares common antigens.