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, angiogenin has also been purified from normal plasma 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. 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; however, it appears not to be sufficient