Copper is an essential element while Cd is an extremely toxic heavy metal of questionable biological usefulness. Cadmium has been reported to interfere with the metabolism of Cu, be teratogenic, and decrease blood flow in the fetal placenta. Because of these reported biological interactions of Cd and Cu, this investigation was conducted to determine the effects of Cd on placental transport of 67Cu and placental blood flow in the guinea pig. All guinea pigs used were 60 +/- 1 days pregnant. A placental perfusion technique was used to measure the maternal-to-fetal clearance of 67Cu and 3H2O across the placenta. The clearance of 3H2O served as an indicator of placental blood flow on the maternal side of the circulation. The results indicated that an iv injection of 1 mg Cd/kg body weight resulted in an immediate increase in the clearance of 67Cu which declined over the next 8 min to an elevated level compared to the extrapolated best-fit curve of control values. This iv injection of CdCl2 concomitantly reduced the maternal-to-fetal clearance of 3H2O across the placenta. In conclusion, an acute exposure of the pregnant female to CdCl2 results in an increased maternal-to-fetal clearance of 67Cu and a reduced placental blood flow that can alter the supply of nutrients to the developing embryo or fetus, and therefore modify normal development.