Ribonucleoside-vanadyl complex is a potent inhibitor of various ribonucleases (1,2,3). This complex is compatible with cell fractionation methods as well as sucrose-gradient centrifugations. The 200 mM stock solution is reconstituted to a green-black clear solution by incubating the sealed vial at 65°C. Once open, the entire sample should be aliquoted into smaller samples and frozen.