We characterized the general properties of the heat shock response in Bacillus subtilis W168, B. subtilis JH642, and an spo0A mutant by using pulse-labeling of bacterial proteins and one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The transfer of cells from 37 to 50 degrees C repressed synthesis of most cellular proteins and led to the induction of at least 26 distinct heat shock proteins after about 3 min. Ethanol (4% [vol/vol]) induced a similar set of proteins, but somewhat more slowly. Synthesis of the majority of heat shock proteins at 50 degrees C returned to a steady-state level 20 to 40 min after the shock. Although no B. subtilis heat shock protein has yet been extensively characterized, three of these proteins were found to be immunologically related to the Escherichia coli heat shock proteins Dnak, Lon, and GroEL. Synthesis of both sigma 28 and sigma 43 proteins was sharply reduced during heat shock. Although a spo0A amber mutation blocks transcription from promoters used by at least two minor B. subtilis sigma factors, it did not alter the kinetics or general properties of the heat shock response.