A previously characterised promoter region upstream from the Bacillus subtilis argC gene was sequenced. The in vivo position of transcription start point (+1), was determined by mung-bean-nuclease mapping. The nucleotide (nt) sequences in the ‘−10’ (TATAAT) and ‘−35’ (TTGAAT) regions closely resemble consensus promoter sequences recognised by B. subtilis σ 43 and Escherichia coli σ 70 RNA polymerases. Between +9 and −64 are three imperfect inverted repeats with high homology to the E. coli arginine biosynthetic gene putative operator sequences (ARG boxes) [Cunin et al., Nucl. Acids Res. II (1985) 5007–5019] and which contain variable intra-repeat distances. Upstream from the ‘−35’ region, extending as far as −71, is a 97% AT-rich sequence. The argC mRNA has a short leader region containing a B. subtilis ribosome-binding site 8 nt upstream from a TTG start codon for an open reading frame (ORF). The deduced amino acid sequence for this ORF contains regions of homology to that for the E. coli argC N-terminal region.