We have investigated the functional characteristics of term human placental villous explants kept in long-term (7–11 days) culture. Fragments of placental villous tissue (∼5–10 mg wet wt) were cultured in supplemented CMRL-1066 culture medium for up to 11 days. After the first day of culture, the syncytiotrophoblast appeared vacuolated and eventually degenerated. However, a new syncytiotrophoblast developed by day 4, being indistinguishable from that of a fresh placenta by 11 days. Release of human chorionic gonadotrophin increased and activity of lactate dehydrogenase in culture medium decreased with culture time. Transport variables were measured over the first 7 days of culture. Basal⁸⁶Rb efflux was reduced with time in culture and was inhibited by Ba²⁺, suggesting the efflux was mediated by K⁺ channels. At all stages of culture, ⁸⁶Rb efflux was stimulated by ATP, hyposmotic medium, and ANG II. A complex pattern of efflux changes with culture time and type of stimulator was observed, suggesting that several compartments of the tissue contributed to stimulated efflux. This culture system provides opportunities for studies of chronic regulation of placental function.