The qualitative pattern of control for 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthetase is a stable and strongly conserved trait of related bacteria and constitutes a reliable generic character. In Bacillus, the generic control pattern for DAHP synthetase is sequential feedback inhibition, a regulatory pattern in which branch-point metabolites are feedback inhibitors. Member species of this genus have DAHP synthetases which vary quantitatively in the effect of temperature upon the sensitivity of the enzyme to feedback inhibition by prephenate. The magnitude of this temperature effect has been expressed quantitatively as the allosteric temperature ratio. The species clusters definable by allosteric temperature ratios correlate exceedingly well with subgroups previously distinguished on the basis of sporangial structure. Hence, two independently derived arrangements of Bacillus subgroups, depending upon very different methodologies, matched for all but 3 of the 24 species considered. The taxonomic position of these subgroups of the genus Bacillus is discussed.