The antibody responses to membrane and early antigens and thymidine kinase of varicella-zoster virus (VZV) were studied in sera during both varicella and zoster by a test with fluorescent antibody to membrane antigen (FAMA), staining the biochemically transformed cells by the immunofluorescent technique and neutralization of virus-specific thymidine kinase activity, respectively. Similar increases in FAMA antibody titers were demonstrated in sera from patients with varicella and zoster. IgM was detected in both groups, but appeared earlier during varicella than during zoster. Furthermore, the antibody titers to early antigens and virus-specific thymidine kinase were higher in patients with zoster than in those with varicella. These data suggest that different types of antibody responses occur during varicella and zoster.