Immunocytochemical and ultrastructural methods were used to investigate the distribution of a family of structural proteins in the human placenta near term. These reveal the distribution of cytoskeletal and `syncytioskeletal' components that may account for some of the more obvious micromorphological features of placental structure. In the syncytiotrophoblast a potentially supporting structure `the syncytioskeletal layer' is described. It is an apparently continuous and complex polymeric network covering the villous tree, a surface of the order of 10 m$^{2}$ in area in the full term placenta (Aherne & Dunnill 1966). It is suggested that this layer plays a part in morphogenesis of the villous tree.