The relative efficacies of a variety of antiviral drugs against bovid herpesvirus 1 was investigated. (E)-5-(2-Bromovinyl)-2'-deoxyuridine and trifluorothymidine were found to be inhibitory at doses of 0.01 micrograms/ml in in vitro yield reduction and plaque reduction assays. In contrast, acylovir was inactive even at concentrations as high as 1,000 micrograms/ml. Other drugs, including phosphonoformic acid, 9-beta-D-arabinofuranosyladenine, 5-iodo-2-deoxyuridine, and 1-beta-D-arabinofuranosylcytosine were active at concentrations previously shown to inhibit herpes simplex virus. Oral administration of (E)-5-(2-bromovinyl)-2'-deoxyuridine to calves infected with bovid herpesvirus 1 had no effect on the level of virus shedding, clinical signs, or susceptibility to secondary bacterial infection with Pasteurella haemolytica. The reason for this lack of in vivo activity was that sufficient levels of the drug in blood were not achieved by oral administration.