Ribonuclease P from Bacillus subtilis cleaves a Gln-Leu tRNA dimeric precursor from bacteriophage T4-infected Escherichia coli, yielding products identical with those generated by the E. coli RNase P. Using this tRNA dimer as an assay substrate, the RNase of P of B. subtilis was shown to consist of at least two components, one of which bands in CsCl equilibrium buoyant density centrifugation at 1.7 g/ml, characteristic of a protein x nucleic acid complex. Both this component and a second, retrieved from the low density (less than 1.4 g/ml) regions of CsCl gradients, are required for RNase P activity. Enzyme activity is abolished by treating the component of density 1.7 g/ml with insoluble RNase A prior to assay. These observations suggest that the RNase P of B. subtilis, like that of E. coli, contain a RNA component essential for activity. That this RNA component is of functional importance, and not an artifact of isolation procedures, is supported by the fact that it is observed in these two phylogenetically disparate organisms.