In order to develop a simple in vitro method for assessing adequacy of placental perfusion, umbilical flow was measured in placentae from 10 normal control women and from 10 women with pre–eclampsia, by infusing through the umbilical arteries a heparinized 0.9% saline solution. The average induced umbilical flow in placentae from uneventful pregnancies was 276 ±16 SE ml/min compared with 163±12 ml/min (p>0.001) in the pre-eclamptic group. In angiographic studies, 79±2 SE % of the cotyledons from the normal series, and only 56±3 % (p>0.001) from the pre-eclamptic series were functional. Additionally, gross and histological examination revealed three distinct types of cotyledon. Placental areas that blanched following saline infusion showed no blood in the collapsed villi or in the intervillous space; areas distinguished by a ruddy appearance following perfusion showed blood trapped in the villi and in the intervillous space; in a third area, the findings were mixed. When compared with placental zones identified by perfusion with 5% Hypaque solution, these three anatomical regions corresponded to normal, reduced, or absent flow (blanched, intermediate, or ruddy regions, respectively). We conclude that under the conditions of this in vitro study, pre–eclamptic placentae had a greater proportion of umbilical perfusion deficits than had normal placentae.