Angiogenin (ANG) was initially purified from serum-free media conditioned by growth of a human adenocarcinoma cell line HT-29 based on its ability to initiate vascularization in the chicken embryo chorioallantoic membrane. A number of other tumor, as well as normal, cell lines can also secrete Angiogenin. In addition, Angiogenin is present in normal human plasma at levels as high as 60-120 ng/mL. Surprisingly, Angiogenin has been found to be a member of the ribonuclease superfamily with approximately 35% sequence similarity at the amino acid level with pancreatic RNase. Angiogenin exhibits ribonucleolytic activity that is distinctly different than that of pancreatic RNase A. The ribonucleolytic activity of Angiogenin toward most RNase A substrates is?much lower than that of RNase A. Nevertheless, the ribonucleolytic activity of Angiogenin is essential to its angiogenic activity since inhibition of the Angiogenin RNase activity will also abolish angiogenesis activity. The activity of recombinant mouse ANG was measured by its ribonucleolytic activity toward RNA. The result was shown in figure 1, and the rmANG produces a delta Abs260/μg?>1.0 in two hours.