RSV is a major cause of lower respiratory tract infections in infants. Higher titers of transplacentally derived maternal antibodies are associated with a relative protection aganist severe RSV disease in young infants. We investigated the use of guinea pigs (Gp) for the study of maternal immunization for the control of RSV infections. Gps were attractive for use in these studies because like humans they have a prenatal transfer of antibodies to their offspring and Gps are susceptible to infections with RSV. Two groups of 35-45 day gestation Gps were immunized intranasally with either 106 PFU A2 strain virus (group A, 3 females) or mock infected preparation (group B, 2 females). Newborns in both groups were challenged with 106 PFU A2 virus intranasally at < 48 hours of age. At 5 days post challenge, viral titers in lung tissue (PFU/gm) were determined. No virus was detected in the lungs of the 8 group A pups (mean log titer ± SD = 1.69 ± 0 with 1.69 representing the lower limit of detection), whereas virus was detected in the lungs of 5 of 6 group B pups (mean log titer ± SD = 3.42 ± 0.9; p = 0.0002 for group A vs B). For the group A animals, serum RSV ELISA antibody titers (mean ± SD) were 3.9 ± 0.4 for the mothers and 3.9 ± 0.2 for the pups. No antibody was detected in group B mothers or pups. These data show that there was a transfer of protective immunity from RSV immunized females to their pups. The Gp model should be useful for the investigation of maternal immunization for protection against RSV infections in infancy.