Lecithin release from fetal membranes and placental tissue was assayed in basal conditions as well as under betamethasone administration. In the absence of the steroid, amnion and chorion released lecithin as a function of incubation time. Both tissues responded to betamethasone by increasing the lecithin release, the amnion exhibited a higher basal level and a greater responsiveness to the hormone than the chorion. Basal lecithin release from placental tissue was unaffected by any steroid concentration.