Embryos and neonatal offspring of wild-captured cotton rats (Sigmodon hispidus) and white-footed mice (Peromyscus leucopus) were tested for the presence of Bartonella spp. Isolates of Bartonella spp. were obtained from 18 of 31 embryos and 7 of 19 neonates from bacteremic dams of the two species; no isolates were obtained from material from non-bacteremic dams. Sequence analysis demonstrated that the isolates from embryos and neonates matched the phylogenetic group of Bartonella spp. isolates obtained from the mother. No antibodies to homologous Bartonella spp. antigens were detected in maternal and neonatal blood or embryonic tissue. These findings suggest the possibility of vertical transmission of Bartonella spp. among natural rodent hosts.