The main early and late transcription termination sites in vivo in bacteriophage 429 DNA were determined by nuclease Si mapping. Transcription of the +29 early genes located at the left end of the viral genome terminated at the very end of the DNA molecule and within the HindIlI G fragment of the viral DNA. Transcription termination of the early genes located at the right end of the genome and that of the late viral genes overlapped in a specific region of the +29 DNA within the EcoRI D fragment. Stem-loop structures followed by uridine-rich tails could be derived close to the 3' ends of early and late mRNAs, suggesting Rho-independent transcription termination in 429 DNA.