Heat-inducible DNA fragments of Bacillus subtilis were cloned with two different promoter probe vectors. The increased synthesis of the reporter enzymes seemed to be due to a transient increase in the transcription of the encoding genes. The structure of the heat-sensitive promoters resembles the consensus sequence of promoters recognized by the vegetative form of RNA polymerase of R subtilis. Our results support data in literature that the heat shock response of B. subtilis is regulated by a different mechanism than in Escherichia coli, where alternative sigma factors direct the transcription of heat shock genes.