Several biological systems originating in the fetus and in the mother are involved in embryo implantation, maintenance of the pregnancy, protection of the fetus against outside influences and the start of labour (these are the immune system, endocrine system, and the endothelial system). In order to work efficiently there has to be some co-ordination. Cytokines which were first described by immunologists make it possible for information between the systems to be exchanged. The authors, referring to recent publications, show that there are several cytokines with specific receptors at the feto-placental interface. The place and the physiological role of these molecules in co-ordinating the links are discussed. These cytokines can be involved in many pathological situations.