To study the mRNA found in sheep omasal epithelium encoding for a peptide transport protein(s), a 446-bp cDNA fragment was cloned from sheep omasal epithelium RNA. The predicted amino acid sequence of this fragment was 85.8, 90.5, and 90.5 percent identical to rabbit, human, and rat PepT1, respectively. The fragment was radiolabeled for use as a probe to study the distribution of the mRNA in various tissues. Total RNA was extracted and mRNA was isolated from the epithelium of gastrointestinal segments and other tissues as indicated. Northern blot analysis was conducted using the radiolabeled probe. In sheep (5) and lactating Holstein cows (3), hybridization was observed with mRNA from the omasum, rumen, duodenum, jejunum, and ileum. The estimated size of mRNA was 2.8 kb. No hybridization was observed with mRNA from the abomasum, cecum, colon, liver, kidney, and semitendinosus and longissimus muscles of either species or the mammary gland of the dairy cows. In pigs (6), the probe hybridized with mRNA from the duodenum, jejunum, and ileum. There was no hybridization with mRNA from the stomach, large intestine, liver, kidney, and semitendinosus and longissimus muscles. Two bands, 3.5 and 2.9 kb were observed with northern blot analysis, indicating two RNA transcripts that may result from alternative mRNA processing. In both Leghorns (15) and broilers (20), the strongest hybridization was found in the duodenum while the jejunum and ileum showed faint bands. The size of mRNA in chickens was 1.9 kb. Other tissues, including the crop, proventriculus, gizzard, ceca, liver, kidney, and muscles showed no hybridization to the probe. In conclusion, mRNA for a peptide transport protein(s) is present in the small intestine of all animals examined and the omasal and ruminal epithelium of sheep and dairy cows. The size of the mRNA varied among species.