Bacillus subtilis mutants with null mutations in the spo0 A gene are resistant to oxidative stress during the exponential phase of growth. This resistance phenotype can be suppressed by mutations in the abrB gene, or in the hpr gene. Both of these gene products are negative regulatory proteins which are over-produced in a spo0 A strain, and the over-production of the hpr gene product results from over-production of the abrB gene product. The results suggested that the resistance to oxidative stress in a spo0 A strain is due to the lack of a protein directly controlled by the hpr negative regulator. Other mutations in the spo0 A gene conferring resistance to ethanol stress (eth) or suppressors of sporulation phenotypes (sof) had no effect on the sensitivity to oxidative stress of strains bearing them.