Forty erythromycin-resistant mutants ofBacillus subtilisstrain 168 were isolated as spontaneous mutants or after induction with 2-aminopurine. They showed different levels of resistance and six of these mutants were studied genetically using transformation reactions. Recombination of some pairs of mutations has a synergistic effect on resistance. All six mutants are clustered on theB.subtilischromosome between the genesstrconferring streptomycin resistance andpurB determining purine biosynthesis. Some mutations overlap at the same site. The genetic order of theseerymutations with respect to one another and a streptomycin-resistant mutationstrhas been determined.