In an attempt to identify substrate proteins of the FtsH metalloprotease involved in stage 0 of sporulation in Bacillus subtilis, the proteome of an ftsH wild-type strain was compared to that of an ftsH null mutant by the 2D gel technique. One of the most abundant proteins identified in the absence of ftsH turned out to be Spo0M, a sporulation control protein of stage 0. Using transcriptional fusion between the spo0M promoter and the bgaB reporter gene, expression analysis did not reveal any influence of FtsH on spo0M transcription, suggesting that FtsH might have a negative effect on the stability of Spo0M due to its proteolytic activity on Spo0M. Indeed, in vitro incubation of purified components demonstrated that Spo0M was degraded by FtsH, indicating that it serves as a substrate for the FtsH protease. These results are discussed.