Summary A procedure is described for preparation of complement-fixing antigens for the varicella-zoster (V-Z) virus in human fetal diploid skin and muscle cell strains. These cells are highly susceptible to the cytopathic effect of the V-Z virus, and can be maintained without a fluid change for the entire period required by the virus to produce complete cellular degeneration. Most of the specific antigen elaborated in the cultures was found to be cell-associated, and relatively high-titered antigens (1:32 and 1:64) were prepared by 50-fold concentration of the cellular phase of infected cultures. Antigens were usually free from anticomplementary activity, but when they were not, the activity could be abolished by treatment with inactivated guinea pig complement.