Antibody-dependent cell-mediated cytotoxicity (ADCC) against Varicella zoster (VZ) infected fibroblasts is described. ADCC requires antibody to VZ and is greater with heavily infected targets. It is not dependent on the immune status of the effector cells. The effector cells responsible for ADCC are present in sheep red cell (E) positive and E-fractions of peripheral blood, and in the G10 non-adherent population. The ADCC activity is present in microexudate non-adherent cells and in the adherent population to a lesser extent. The technique provides a means to study host defence against VZ infection in immune compromised individuals.