This paper describes a method for the culture of rat placental cells. The method involved separation of the basal layer from the labyrinth and sequential digestion of the cells. The cells were demonstrated not to be fibroblasts and are described in terms of their appearance under the light and electron microscopes. Transferrin and iron uptake by the cells was examined and compared with results achieved using other methods of study. The results showed that transferrin bound to receptors on the cell surface and that the transferrin, once bound, was taken into the cell. Only this internalized transferrin was capable of donating iron to the cells. The iron was accumulated within the cells and did not appear to be released to the incubation medium. The apparent dissociation constant (Ka) for transferrin was found to be 6.96 X 10(6) M-1, a value similar to that described by earlier workers. The placental cells had 3.4 X 10(11) binding sites/microgram DNA, equivalent to approximately 1 X 10(6) sites/cell. From these data, and from the rate of accumulation of iron by the cells, the receptor turnover time was estimated as being between 5 and 10 min.