Woodchucks were trapped and blood samples collected to determine the prevalence of WHV [woodchuck hepatitis virus] in natural woodchuck populations. Sera from 217 woodchucks trapped from southeastern Pennsylvania, central New Jersey and north central Maryland, USA, during the spring and summer of 1978 and 1979 were tested for evidence of WHV infection. In 1978, 7 of 51 (13.7%) woodchucks were positive for WHV antigens and in 1979, 28 of 166 (16.9%) tested positive. Of 166 (29.5%) woodchucks trapped in 1979, 49 had antibodies to WHV antigens. A high prevalence of WHV in woodchucks from the areas surveyed is indicated.