The alternative sigma factor sigmaB has an important role in the acquisition of stress-resistance in many gram-positive bacteria. In the foodborne pathogen Bacillus cereus sigmaB is activated strongly upon a heat shock and other stress conditions. Here we describe the identification of the set of sigmaB-regulated genes in B. cereus by DNA microarray analysis of the transcriptome upon a mild heat shock. A total of 24 genes could be identified as being sigmaB-dependent as witnessed by (i) significantly lower expression-levels of these genes in mutants deleted for sigB and rsbY (encoding the alternative sigma factor sigmaB and a PP2C phosphatase that acts as a crucial positive regulator of sigmaB-activity, respectively) than in the parental strain B. cereus ATCC 14579, and (ii) increased expression of these genes upon a heat shock. Newly identified members of the sigmaB-regulon of B. cereus include an ECF-sigma factor (sigmaZ), a histidine kinase and two genes that have predicted functions in spore germination. Our data indicate that the sigmaB-regulon of B. cereus is considerably smaller than that of other gram-positive bacteria. This appears to be in line with phylogenetic analyses of sigmaB in which sigmaB in the B. cereus group was suggested to be close to the ancestral form of sigmaB in gram-positive bacteria.