It is generally accepted that transferrin receptor is located in the endothelial cells of the brain, but its existence in other brain cell types is less established. In this study, a [¹²⁵I]transferrin binding assay was used to determine whether there is transferrin receptor on the membrane of cultured rat cortical astrocytes (type 1) in vitro. The results demonstrated that cortical astrocytes (type 1) in suspension attracted [¹²⁵I]transferrin with a saturable and specific binding. Scatchard and Hill plot analysis showed that the dissociation constant (K_D) of the binding was about 3.5×10^–8 M and the number of receptors was about 7.1×10⁴/cell. The Hill coefficient was 0.99, approaching 1, indicating the absence of cooperativity. The receptor was specific both for rat and human transferrin. The binding of rat [¹²⁵I]transferrin could be competitively and specifically inhibited by unlabeled iron-saturated rat and human transferrin, and no difference was found between interaction of rat or human transferrin with this receptor. The interaction of duck or camel transferrin with this receptor was found to be very weak. This study provides evidence for the presence of transferrin receptor on the plasma membrane of cultured rat brain astrocytes.