Among varicella-zoster virus (VZV)-immune adults aged 20 to 35 years, T lymphocytes producing interferon-gamma (IFN-gamma) in response to a VZV antigen stimulus are eight times more numerous than those making interleukin-4 (IL-4). In persons over 55 years old, the frequency of IFN-gamma-making cells falls while the number of IL-4-making cells remains roughly constant. The persistence of IL-4-making cells may contribute to the maintenance of IgG antibodies to VZV with aging.