Streptococcus agalactiae or group B streptococci (GBS) are gram-positive diplococci and are the leading bacterial cause of pneumoniae, sepsis, and meningitis in neonates. Neonatal GBS infections may occur prior to or during birth. GBS have been cultured from the chorioamnionic membrane of pregnant women and have therefore been associated with chorioamnionitis and premature labor. A potential route for GBS to establish infection of a neonate would be to penetrate the placental membrane of colonized pregnant women. In our laboratory, we have constructed in vitro systems to emulate certain events during the colonization and invasion of host epithelial cell tissues by GBS. By utilizing techniques to grow primary cultures of both chorion cells and amnion cells isolated from human C-section placentas, we have established a relevant model to investigate certain aspects of GBS adherence and invasion into the placental membrane. To identify relevant molecules required for GBS to colonize the multiple tissues it encounters during an infection, we have applied a variety of biochemical approaches with host cell membrane preparations as well as purified extracellular matrix proteins. These techniques are enabling us to further characterize the pathogenic mechanisms utilized by GBS.