Abstract
Vaccinia and pseudorabies viruses are resistant to ACV [Acyclovir or 9-(2-hydroxyethoxymethyl)guanine] in normal cells. However, both viruses are sensitive in thymidine kinase (TK)-transformed cells in which the resident HSV-specific TK is able to phosphorylate the drug. This demonstrates the sensitivity of these viruses to phosphorylated ACV and suggests a wider antiviral activity for the phosphorylated drug.