Analysis of a mutant in fam, a pleiotropic gene affecting cell division in Escherichia coli, revealed that this gene is probably identical to the heat shock regulatory gene htpR. The fam-715 mutant and different htpR mutants were found to share the following three characteristics: temperature-sensitive growth, faulty cell division, and inability to induce the normal cellular heat shock response. These defects were all corrected in fam and htpR mutants by complementation with plasmids carrying intact htpR+ or by recombination between these mutant alleles and a plasmid carrying only a portion of htpR. These results implicate the E. coli heat shock system in the regulation of cell division and raise the question of a similar role in other organisms.