Two ribonucleases (RNase Phya and RNase Phyb) were purified to homogeneity on SDS-PAGE from the culture filtrate of the fungus Physarum polycephalum. The apparent molecular weights of RNases Phya and Phyb were about 20,000. The pH optima of these two RNases were around 4.5-4.75. The RNases released