We have isolated a rifampicin-resistant mutant of Escherichia coli RNA polymerase that restores transcription termination in strains with a defective rho protein. In such strains, the mutant RNA polymerase terminates transcription at normally rho-dependent sites at the end of the trp operon, in bacteriophage lambda, and within the lac operon. In addition, a strain with this mutant RNA polymerase remains viable with an amber mutation in rho, whereas a strain with wild-type RNA polymerase does not. These results suggest that the mutant RNA polymerase can terminate transcription at normally rho-dependent sites in the absence of rho.