Two homogeneous samples of low molecular mass RNAase (RNAases Bci I and Bci II) were obtained from cultural filtrates of spore-forming bacteria strain Bacillus sp. BCF 247 isolated from permafrost soils. The yields of RNAases Bci I and Bci II were 17% and 16% at the 17388- and 15376-fold degree of purification, respectively. Both enzymes have a close specific activity which is equal to approximately 4.7 x 10(-5) activity units per mg of protein. The relative molecular masses of the isolated proteins were determined and their N-terminal amino acid sequences identified. It was shown that the higher molecular mass sample of the enzyme is a pro-RNAase which, in contrast with the mature protein, contains an additional decapeptide segment in the N-terminal part of its molecule. The structure of RNAase Bci was compared with that of RNAases obtained from other Bacillus species; its ability to interact with a natural intracellular inhibitor of B. amyloliquefaciens RNAase was demonstrated.