The sensitive varicella-zoster fluorescent antibody to membrane antigen (V-Z FAMA) test was used in a seroepidemiologic survey of two outbreaks of varicella involving 30 children. The attack rate of varicella based on clinical observations alone was 60%. The attack rate based on clinical and serological observations lay between 78% and 82%, after excluding those children who had detectable antibody at the time of exposure. No subclinical varicella infection was observed in this small series of patients. No boost in antibody response was observed in immunes who were exposed to varicella. No patients with detectable V-Z antibody by FAMA at the time of exposure developed clinical varicella. The V-Z FAMA test provided helpful information about the immune status of persons exposed to varicella.