We present data which map the 5' and 3' ends of transcripts of the natural ovalbumin gene. First, hybridization of radiolabeled 5' and 3' fragments of the gene to oviduct nuclear RNA which had been electrophoresed in agarose gels and transferred to DBM paper localized the 5' and 3' ends of precursor molecules and demonstrated that the largest ovalbumin RNA molecules detectable by this method (approximately 7.8 kb) were similar in size to the ovalbumin natural gene. Second, hybridization of end-labeled probes to oviduct nuclear RNA followed by digestion with S1 nuclease and analysis on polyacrylamide gels mapped more precisely the 5' and 3' ends of the precursor molecules, and these termini were coincident with the beginning and end of the structural sequence of the natural gene. These results suggest that the 7.8 kb precursor is likely to be the primary transcript of the ovalbumin gene.