Antiogenin is a potent blood vessel-inducing polypeptide that has a unique ribonucleolytic activity. Initially identified from tumor cells conditioned medium through its ability to induce neovascularization in the chick embryo chorioallantoic membrane assay [1], angiogenin has also been purified from normal plasma [2] which suggested that it might be involved in endothelium homeostasis. Angiogenin is highly homologous to pancreatic ribonuclease A with 68% amino acid sequence homology and conserved essential active site residues [3]. However, angiogenin is inactive in standard ribonuclease assays but has a ribonucleolytic specificity toward ribosomal and transfer RNAs [4]. This enzymic activity might be relevant to the process of angiogenesis since a functional active site seems necessary for the expression of its angiogenic property [5]; however, it appears not to be sufficient [6].