Cellular receptors are required for efficient entry of retroviruses into cells. We previously cloned a chicken gene responsible for susceptibility to the retrovirus subgroup A Rous sarcoma virus (RSV(A)). Here we have isolated the quail homolog and generated two alternatively spliced processed genes encoding cellular receptors for RSV(A). Predicted products of the processed genes appear to be small membrane-associated proteins with identical 83 amino acid extracellular domains but different membrane anchors. Within the extracellular domain is a region closely related to the ligand-binding repeat of the low density lipoprotein receptor (LDLR). Expression of either processed gene renders mammalian cells specifically susceptible to RSV(A). Antibodies directed against the receptor block subgroup A infection of avian cells via endogenous receptors and have no effect on entry of other RSV subgroups. Thus, small LDLR-related proteins are cellular receptors for RSV(A).