Persistent infection was established in Vero cells inoculated with varicella-zoster virus (VZV)-infected WI-38 cells. Treatment with 9-(2-hydroxy-ethoxymethyl)guanine (acyclovir) at doses of 100, 80, 40, and 10 micrograms/ml eliminated the infectious virus, lower doses such as 0.1 and 0.01 micrograms/ml were ineffective.