Andes virus (ANDV) causes a fatal hantavirus pulmonary syndrome (HPS) in humans and Syrian hamsters.Human ␣ v  3 integrins are receptors for several pathogenic hantaviruses, and the function of ␣ v  3 integrins on endothelial cells suggests a role for ␣ v  3 in hantavirus directed vascular permeability. We determined here that ANDV infection of human endothelial cells or Syrian hamster-derived BHK-21 cells was selectively inhibited by the high-affinity ␣ v  3 integrin ligand vitronectin and by antibodies to ␣ v  3 integrins. Further, antibodies to the  3 integrin PSI domain, as well as PSI domain polypeptides derived from human and Syrian hamster  3 subunits, but not murine or bovine  3 , inhibited ANDV infection of both BHK-21 and human endothelial cells. These findings suggest that ANDV interacts with  3 subunits through PSI domain residues conserved in both Syrian hamster and human  3 integrins. Sequencing the Syrian hamster  3 integrin PSI domain revealed eight differences between Syrian hamster and human  3 integrins. Analysis of residues within the PSI domains of human, Syrian hamster, murine, and bovine  3 integrins identified unique proline substitutions at residues 32 and 33 of murine and bovine PSI domains that could determine ANDV recognition. Mutagenizing the human  3 PSI domain to contain the L33P substitution present in bovine  3 integrin abolished the ability of the PSI domain to inhibit ANDV infectivity. Conversely, mutagenizing either the bovine PSI domain, P33L, or the murine PSI domain, S32P, to the residue present human  3 permitted PSI mutants to inhibit ANDV infection. Similarly, CHO cells transfected with the full-length bovine  3 integrin containing the P33L mutation permitted infection by ANDV. These findings indicate that human and Syrian hamster ␣ v  3 integrins are key receptors for ANDV and that specific residues within the  3 integrin PSI domain are required for ANDV infection. Since L33P is a naturally occurring human  3 polymorphism, these findings further suggest the importance of specific  3 integrin residues in hantavirus infection. These findings rationalize determining the role of  3 integrins in hantavirus pathogenesis in the Syrian hamster model.