Trophoblast cells coordinate the activities of maternal and embryonic tissues by secreting hormones, cytokines, and various growth factors that selectively and specifically gain access to maternal and embryonic compartments. Abnormalities associated with trophoblast cell growth, differentiation, or function result in impaired embryonic development. The Serono Symposia, USA conference "Trophoblast" "Cells: Pathways for Maternal-Embryonic Communication," August 6-9, 1992, provided a forum for morphologists, cell biologists, endocrinologists, and molecular biologists to present the most current research on understanding the complexities of the trophoblast cell signaling system.