Microflora of the small intestine of sheep was examined. Samples of tissue and digesta were taken from four sites along the small intestine (3, 8, 13, and 18 m from the pylorus) and maintained under anaerobic conditions. The pH of the digesta taken at the 3rd, 8th, 13th, and 18th m sections were 5.44, 6.37, 7.24, and 6.79. Digesta and tissue samples were diluted serially and plated within the anaerobic glove box on complex medium containing rumen fluid. In addition, each sample was plated on the same medium and incubated aerobically. As determined by growth under anaerobic conditions, viable counts of the digesta ranged from 5 X 10(4) to 7 X 10(6) cells/g, whereas counts for the tissue ranged from 2 X 10(2) to 4 X 10(4) cells/g. Viable counts determined aerobically for the digesta ranged from 1 X 10(4) to 5 X 10(6) cells/g, whereas the counts for the tissue ranged from 5 X 10 to 6 X 10(4) cells/g. Tentative identification of 50 isolates from samples of tissue and digesta in the 13th m section revealed a predominance of streptococcal organisms and rod shaped organism morphologically similar to Propionibacterium. An indigenous population of acid-tolerant bacteria with the ability to ferment simple sugars and starch was in the small intestine.