The effects of maternal infections with guinea pig cytomegalovirus (CMV) at different stages of gestation were evaluated in mothers, fetuses, and newborn animals. Increased cervical excretion of guinea pig CMV was detected in pregnant animals one to 30 days after inoculation. Fetal infection occurred in utero regardless of the time of maternal infection. The frequencies of stillbirths and viral infection in newborn offspring were higher in mothers infected in late gestation than in mothers infected during the first trimester of pregnancy. The major factor affecting isolation of guinea pig CMV from offspring was the duration of maternal infection. Virus was detected most often in fetuses and newborn animals within two weeks after inoculation of the mothers. Thereafter, guinea pig CMV disappeared progressively in the progeny, although histological lesions were observed and virus was found in the salivary glands of some offspring for as long as 14 weeks after delivery.