A murine model of the cytotoxic T lymphocyte (CTL) response to glycoprotein B (gB) of human cytomegalovirus (HCMV) was developed based on the use of adenovirus (Ad) and vaccinia virus (Vac) recombinants expressing gB. Mice of different major histocompatibility haplotypes [CBA (H-2k), BALB/k (H-2k) and BALB/c (H-2d)] infected with the Ad-gB recombinant developed an Ad-specific CTL response. However, only the H-2k mice developed a significant HCMV gB-specific CTL response, as indicated by the major histocompatibility complex class I-restricted lysis of Vac strain Copenhagen (VacC)-gB recombinant-infected target cells by H-2k mouse immune spleen cells. The VacC-gB recombinant elicited only a weak gB-specific CTL response in these mice, indicating that the observed gB-specific CTL response in mice is dependent on the expression vector used for immunization. The gB-specific cytotoxicity observed in H-2k mice was mediated by the CD8 lymphocyte subset.