The villous syncytium of the placenta of the macaque was found to contain channel-like formations bounded by syncytial membrane. They were present in placental specimens obtained from rhesus monkeys at periods of gestation varying from 90 to 164 days and were identifiable only by electron microscopy. These syncytial channels communicated with the intervillous space but were quite distinct from junctional complexes described in the syncytium of human placental villi. They appeared to be extensions of the intervillous space whereby areas of the syncytium would come in contact with maternal plasma flowing at a greatly reduced rate. Features of these channels, of their bounding membrane and of the adjacent cytoplasm, could point to a phenomenon of regional specialisation in the syncytiotrophoblast.