Three alkaline RNases were purified from human pancreatic juice to near homogeneity as judged by sodium dodecyl sulfate and native polyacrylamide gel electrophoreses. The molecular weights of these RNases determined by sodium dodecyl sulfate electrophoresis were 27,000, 19,000, and 13,000. The activities of these three RNases were increased by addition of Mg2+, Ca2+, Co2+, K+, Na+, spermine, and spermidine and decreased by the addition of heparin, Cu2+, and Zn2+. These RNases showed higher hydrolytic activity toward polycytidylic acid than toward polyguanylic acid, polyuridylic acid, or polyadenylic acid. The three human pancreatic RNases were immunologically identical but differed from human liver RNase, as shown by Ouchterlony double-diffusion test. Radioimmunoassay of human pancreatic RNase showed that immunologically similar RNases are present in human saliva, and serum.