The nature and origin of soluble proteins from human amniotic fluid have been investigated by gel filtration chromatography on Sepharose 6B and ion-exchange chromatography on Ecteola-cellulose. Each fraction has been studied by immunoelectrophoresis. Specific antisera against serum proteins, amniotic fluid proteins, fetal proteins and salivary proteins have been used. These various antisera showed that the amniotic fluid contains maternal proteins, but also more specific proteins from fetal origin such as β 2-microglobulin, urinary mucopolysaccharides, salivary proteins and carcinoembryonic antigen. These results not only confirm that amniotic proteins are essentially from maternal origin, but prove the important fetal contribution and emphasize the importance of the fetoplacental unit in the monitoring of high risk pregnancies.