Laminin was localized by immunohistology to stromal cells of the human non-pregnant endometrium as well as to similar cells of the decidua. Only small amounts of laminin were detected during the proliferative phase, but significant quantities had accumulated by the mid-secretory phase which persisted in decidua if pregnancy occurred. This cyclical variation suggested hormonal control of laminin production. The presence of laminin could also be demonstrated in decidual cells in culture, most of which was intracellular or pericellular with very little liberated into the culture supernatant. Human first trimester trophoblast cells were observed to attach preferentially to laminin-coated surfaces in vitro. The role of laminin in trophoblast-decidua interaction in vivo is discussed.