Three additional alleles of the outB gene of Bacillus subtilis, whose activity is required for spore outgrowth, were identified. The nucleotide sequence of three mutant genes was determined. Analyses of dominance-recessivity showed that the wild-type allele is dominant over the mutant ones. When the outB gene was placed under the control of the inducible spac-1 promoter, the presence of IPTG was necessary to obtain normal growth. The results suggested that the outB gene is required for growth of B. subtilis. Expression of outB from the sporulation promoter spoIID negatively affected subsequent spore outgrowth, without altering vegetative growth and sporulation.