A ribosomal ribonucleic acid gene set consisting of genes for 16S, 23S, 5S, and 4S ribonucleic acid species has been genetically mapped to a position between the markers recG13 and abrB74 on the Bacillus subtilis chromosome and designated rrnA. A ribosomal mutation, ksgA, was found to be linked to rrnA. This places rrnA in a region of the chromosome where ribosome-related genes occur but that is not directly adjacent to the major cluster of ribosome-related markers.