Fosprenil suppressed the multiplication of cattle diarrhea virus in calf coronary vessel cell culture. Added to the culture of infected cells in a dose of 200 mg, the drug decreased the virus titer 30-fold in comparison with infected control cultures. Antiviral activity of fosprenil towards infective rhinotracheitis virus multiplication was still higher: in a dose of 100 mg it decreased the virus titer in fetal calf lung culture 100-fold in comparison with the control. Moreover, the cytopathogenic effects of the viruses in infected cultures were 24-48 h delayed under the effect of fosprenil in comparison with infected control cultures. These results recommend fosprenil for the treatment of cattle viral diseases.