One week after infection with a virulent strain of hemorrhagic enteritis virus (HEV), turkeys were vaccinated for Newcastle disease. The effect of a virulent strain of HEV on turkeys' immune response to Newcastle disease vaccine and the mitogenic response of their whole blood peripheral lymphocytes were examined. The results revealed a statistically significant difference (P less than .01) in the Newcastle disease hemagglutination inhibition (NDHI) antibody titers from turkeys infected with virulent HEV. The NDHI antibody titers were lower in turkeys exposed to virulent HEV before vaccination. There was an initial depression in phytohemagglutinin (PHA) response 1 week postinfection in turkeys infected with virulent HEV strain.