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Group B streptococci (GBS) are the most common cause of pneumonia and sepsis during the neonatal period; however, the pathogenesis of this infection is poorly understood. We investigated the ability of GBS to enter epithelial cells in culture. Two strains of GBS were capable of invading immortalized respiratory epithelial cell lines in vitro at different levels, suggesting strain differences in invasiveness. Intracellular replication was not observed. Invasion required actin microfilaments but not microtubular cytoskeletal elements. Active bacterial protein, DNA, and RNA syntheses were required for invasion. These findings are consistent with our previous observation of intracellular GBS in the lungs of infected primates. We hypothesize that this organism may access the bloodstream by direct invasion of the epithelial cell barrier.