Three well-defined E. coli operator regions were examined for recurring conformational deviation from a regular B-DNA helix. All three, the lac, trp, and gal. show repeats of the same set of neighboring helical twist angles. These angles recur with a periodicity equal to the helix periodicity on one side of the operator’s axes of symmetry. The probability that their occurrence is random was found to be extremely small. Therefore, we propose that in addition to specific bases, repeating twist angle patterns are likely to be among the local parameters involved in repressor-operator recognition.