These studies have been conducted as a first step toward investigating the molecular mechanism by which DNA‐dependent RNA polymerase recognizes a specific region of DNA. The DNA moieties are either bound to or freed from RNA polymerase. Results obtained so far indicate that the DNA moieties remaining as resistant segments after deoxyribonuclease digestion should be regarded as the binding regions on DNA. The results described here were carried out by use of E. coli and lambda DNA. Copyright © 1969 Wiley‐Liss, Inc.