An epizootic suspected to be caused by parapoxviruses occurred in winter, 1984-85, among wild Japanese serows (Capricornis crispus) with nodular or papular lesions in Gifu Prefecture, Japan. Virus isolations were attempted on 30 animals using bovine fetal testicle cell cultures. Viral agents growing with cytopathic effects were isolated from six animals. The agents were identified as parapoxvirus from electron microscopic findings and physico-chemical characteristics. Antibody prevalence to the isolated agent, named S-1, was examined by enzyme-linked immunosorbent assay. No antibodies were detected among 153 sera obtained during two winters 1981-82 and 1982-83, but one of 189 sera collected in the winter of 1983-84 was positive. In contrast, 75 (32%) of 237 sera had antibodies to S-1 in 1984-85, when the disease was first detected. Antibody prevalences of 1984-85 were highest (39%) in December 1984, the first month of animal capture, and declined gradually to 20% in March 1985.