To get basic information to control persistent virus infection among domestic animals by cytokines, the antiviral activity of four natural human cytokines against bovine viral diarrhea virus (BVDV) was evaluated. Normal bovine peripheral blood mononuclear leukocytes (PBML) and fetal bovine muscular cells (FBMC) were treated with varying doses of human interferon (IFN)-alpha, IFN-gamma, tumor necrosis factor (TNF)-alpha and TNF-beta. The antiviral activity in treated cells was measured by the titration of virus infectivity in comparison with non-treated controls. IFN-alpha significantly suppressed virus growth in both PBML and FBMC. The growth of two cytopathogenic and two noncytopathogenic strains was suppressed in the presence of more than 10(3) u/ml of IFN-alpha. Addition of either TNF-alpha or TNF-beta to IFN-alpha did not potentiate the suppressive effect. IFN-alpha also suppressed the replication of BVDV in PBML from cattle persistently infected with BVDV.