An indirect immunoperoxidase (ip) technique involving avidin-biotin peroxidase complex, using a monoclonal antibody was developed for the detection of haemorrhagic enteritis (he) virus antigen in frozen and formalin-fixed paraffin-embedded tissue sections. This 1P procedure was compared with an indirect immunofluorescence antibody technique (ifat) and an agar gel precipitation test (agpt). Spleens from turkeys experimentally infected with HE virus were collected and examined for the presence of viral antigen. The IP staining procedure detected HE viral antigen as early as 48 hours after infection and continued to demonstrate the presence of viral antigen for up to 11 days after infection at which time the experiment was terminated. The antigen was detected from three to seven days and from two to nine days after infection by the agpt and ifat, respectively. The ifat and agpt had sensitivities of 74·19 and 48 per cent, respectively, compared with ip. Because of its high sensitivity and specificity, the ip technique could be useful for studying the pathogenesis and rapid laboratory detection of he virus.