Previous analyses of human sera for recognition of gB domains have revealed differential rates of antibody reactivity for the individual antigenic domains. Whereas almost 100% of infected individuals develop antibodies against AD-1, only 50% show reactivity against AD-2 [17] . To obtain information on the frequency of recognition of Dom I and Dom II we determined antibody reactivity against these domains in a larger serum panel of HCMV infected individuals and compared it to the known antigenic domains. A total of 80 randomly selected sera from HCMV seropositive individuals, as determined by a commercially available ELISA test, was analyzed. Ten sera from HCMV negative donors served as controls. Within the serum panel from HCMV-seropositive individuals, reactivity for gB was 100%, underscoring the antigenicity of this protein (Fig. 7) . In accordance with our previous observations, positive reaction with AD-1 was also 100% and 57% of the sera contained antibodies against AD-2 [17] . Dom I was recognized by 55% whereas 94% of the specimens reacted with Dom II. Thus, Dom I and Dom II represent antigenic domains on gB which induce antibodies with high frequency during infection. For the sake of consistency in nomenclature of gB antigenic domains, they were designated AD-4 (Dom II) and AD-5 (Dom I).