The competition between different types of aphthoviruses (foot-and-mouth disease virus [FMDV]) for receptor site utilization was determined. The Southern African Territories (SAT) types of FMDV absorbed poorly to BHK-21 cells as measured by a radioactivity binding assay but grew to relatively high titers on these cells. On BK cells, however, all three SAT types bound well and competed with each other for receptor sites. In addition, unlabeled FMDV types A12 and O1B were able to completely inhibit the binding of 3H-uridine labeled SAT types. Unlabeled SAT, however, was only slightly able to inhibit the adsorption of labeled A12 and moderately inhibit the binding of labeled O1B. Saturation binding studies with homologous virus showed that BK cells contain at least 100-fold more receptor sites for types A12 and O1B than for the SAT types. Competitive binding analysis between type A12 FMDV and poliovirus and encephalomyocarditis virus revealed that these three viruses all used different receptor sites. Thus, different FMDV serotypes appear to utilize both common and unique receptor sites which are different from those of at least two other picornaviruses.