When cells of the yeast, Saccharomyces cerevisiae, were deprived of nitrogen, a condition leading to G1 arrest, there was an immediate increase in the levels of total ribonuclease (RNase) activity within these cells. During starvation, only the cells arrested in G1 showed increased RNase activity. Although the RNase activities of extracts of starved and actively growing cells were similarly influenced by pH, the activities of starved cells were less stable on both storage and heating. Differences were also noted in substrate specificity. The results of this study suggest that arrest within G1 may increase RNase activity. However, all RNases did not appear to be influenced equally, since the total pool of RNase activity from log phase and G1 arrested cells showed differences in stability and substrate specificity.