The Escherichia coli rodA and ftsW genes and the spoVE gene of Bacillus subtilis encode membrane proteins that control peptidoglycan synthesis during cellular elongation, division and sporulation respectively. While rodA and ftsW are essential genes in E. coli, the B. subtilis spoVE gene is dispensable for growth and is only required for the synthesis of the spore cortex peptidoglycan. In this work, we report on the characterization of a B. subtilis gene, designated rodA, encoding a homologue of E. coli RodA. We found that the growth of a B. subtilis strain carrying a fusion of rodA to the IPTG-inducible Pspac promoter is inducer dependent. Limiting concentrations of inducer caused the formation of spherical cells, which eventually lysed. An increase in the level of IPTG induced a sphere-to-short rod transition that re-established viability. Higher levels of inducer restored normal cell length. Staining of the septal or polar cap peptidoglycan by a fluorescent lectin was unaffected during growth of the mutant under restrictive conditions. Our results suggest that rodA functions in maintaining the rod shape of the cell and that this function is essential for viability. In addition, RodA has an irreplaceable role in the extension of the lateral walls of the cell. Electron microscopy observations support these conclusions. The ultrastructural analysis further suggests that the growth arrest that accompanies loss of the rod shape is caused by the cell's inability to construct a division septum capable of spanning the enlarged cell. RodA is similar over its entire length to members of a large protein family (SEDS, for shape, elongation, division and sporulation). Members of the SEDS family are probably present in all eubacteria that synthesize peptidoglycan as part of their cell envelope.