To date, a viral homolog of vascular endothelial growth factor (VEGF) has been discovered in only one poxvirus, namely orf virus of sheep. Orf virus encodes two such proteins, each of which possesses characteristic cysteine spacing motifs found in cellular VEGF family members. Viral VEGF binds to the members of the same family of cell surface receptors as its cellular counterparts and has proangiogenic activity.