The study investigates the role of σB, a secondary sigma factor in *Bacillus subtilis*, during heat shock. σB levels increase 5- to 10-fold when cultures are shifted from 37°C to 48°C. Western blot analyses show that σB, RsbV, and RsbW proteins increase coordinately after heat shock, with this increase dependent on σB but not RsbV. Nuclease protection experiments support the notion that heat shock enhances transcription from the σB-dependent promoter of the sigB operon. The level of mRNA initiating at the σB-dependent ctc promoter also increases 5- to 10-fold after heat shock. Pulse-labeling experiments demonstrate that wild-type and mutant strains produce similar amounts of major heat-inducible proteins, but at least seven additional proteins are present in the wild-type strain after heat shock, which are absent in the σB null mutant. This suggests that σB is not essential for the expression of essential heat shock genes but contributes to the synthesis of several other heat-inducible proteins. The study concludes that σB is a heat-inducible protein and a heat shock σ factor, playing a role in the heat shock response of *B. subtilis*.The study investigates the role of σB, a secondary sigma factor in *Bacillus subtilis*, during heat shock. σB levels increase 5- to 10-fold when cultures are shifted from 37°C to 48°C. Western blot analyses show that σB, RsbV, and RsbW proteins increase coordinately after heat shock, with this increase dependent on σB but not RsbV. Nuclease protection experiments support the notion that heat shock enhances transcription from the σB-dependent promoter of the sigB operon. The level of mRNA initiating at the σB-dependent ctc promoter also increases 5- to 10-fold after heat shock. Pulse-labeling experiments demonstrate that wild-type and mutant strains produce similar amounts of major heat-inducible proteins, but at least seven additional proteins are present in the wild-type strain after heat shock, which are absent in the σB null mutant. This suggests that σB is not essential for the expression of essential heat shock genes but contributes to the synthesis of several other heat-inducible proteins. The study concludes that σB is a heat-inducible protein and a heat shock σ factor, playing a role in the heat shock response of *B. subtilis*.