Lam, K. M. and G. D. Hsiung (VA Hospital, West Haven, Conn. 06516). Herpes-virus infection of guinea pigs. II. Transplacental transmission. Amer J Epidem 93: 308–313, 1971.—A total of 50 female Hartley guinea pigs of various ages were inoculated intraperitoneally with guinea pig herpes-like virus (GPHLV). Twenty-five animals became apparently pregnant; they were sacrificed, and virus was isolated from all of them. Of the 25 litters of fetuses examined, 13 litters showed virus infection (52%). Virus recovery from the fetal tissues was apparently related to the length of infection and the concentration of virus in the maternal tissue and blood. A transplacental transmission was established in a shorter infection time when a larger dose of inoculum was used. There were, no gross abnormalities observed in the 88 fetuses examined with the exception of one with a deformed fore-limb. No notable histopathological change or inclusion bodies were found in either the maternal or fetal tissues examined. The route of transmission of GPHLV from maternal to fetal tissues appears to be hematogenous dissemination. Virus carrying leukocytes may play an important role in this vertical transmission.