The guinea pig (gp) model of congenital cytomegalovirus (CMV) infection was used to evaluate a gpCMV glycoprotein vaccine. Hartley guinea pigs were immunized 3 times with 50 microg of lectin column-purified glycoproteins prepared from gpCMV-infected or -uninfected tissue culture. Immunization with the gpCMV vaccine produced seroconversion in all animals. Animals then were placed with gpCMV-seronegative male animals and were challenged late in pregnancy with virulent salivary gland-passaged gpCMV. Immunization with gpCMV glycoproteins significantly improved pregnancy outcome, with 54 of 63 pups live-born in immunized animals, compared with 21 of 48 in the controls (P<.001). In addition, virus was isolated from 24 of 54 live-born pups born to immunized mothers, compared with 16 of 20 live-born pups born to controls, indicating that immunization significantly reduced in utero transmission in surviving animals (P<.01).