Thirty-five Bacillus brevis strains obtained from culture collections, including protein-producing isolates, were taxonomically studied by using numerical analysis, DNA base composition, and DNA-DNA hybridization. Six DNA relatedness groups were represented, and these groups correlated well with clusters based on the numerical analysis. The B. brevis strains were separated into B. brevis sensu stricto, four new species, and an unidentified species of the genus Bacillus. Bacillus migulanus sp. nov., Bacillus choshinensis sp. nov., Bacillus parabrevis sp. nov., and Bacillus galactophilus sp. nov. are proposed.