During gel filtration and subsequent anion exchange chromatography the nuclease activity from cotyledons of germinating Phaseolus vulgaris L. was eluted as a single peak, containing high RNase and low inherent DNase activities. The RNase activity was unaffected by EDTA and had no particular requirement for mono- or divalent cations, but was substantially inhibited by Mn ++ and Zn ++ . Sodium dodecyl sulphate and the vanadyl ribonucleoside complex were identified as effective inhibitors of the RNase activity. The base preference for homoribonucleic acids was: poly U > poly C > poly A > poly G.