Junin virus infection in guinea pigs is known to be similar to human Argentine hemorrhagic fever (AHF). The guinea pig was chosen as a model for transplacental transmission of Junin virus, as both guinea pig and man have a similar placental structure. Pregnant guinea pigs were infected with the pathogenic XJ strain of Junin virus intramuscularly route at different stages of pregnancy. The group infected during the last third of pregnancy produced 16 newborn, but mortality reached 100%: 18% were born with typical AHF hemorrhagic signs, 54% without signs, and the remainder were stillborn. Virus was recovered from organs of newborns, as well as placental tissues. A second group, infected in the second third of pregnancy, died with intrauterine fetuses, all of which showed hemorrhagic signs and virus present. In a last group, infected in the first third of pregnancy, fetuses were free from macroscopic lesions. In order to determine whether lactation may be an alternative infection route in guinea pigs, mother guinea pigs were infected with Junin virus at different times postparturition. The 84% noninfected newborn housed together with their infected mothers died during the suckling period, half with typical AHF signs. Junin virus transmission from mother to fetus was thus proved, and lactation may be considered as an alternative perinatal infection route.