In 20 healthy Peruvians aerobic cultures were done of upper small bowel contents, obtained following the method of the string capsule or Enterotest, and of faringeal material, obtained doing gargles with sterilized water. In 15 (75%) of the 20 subjects cultures of small bowel contents either were sterile (in 5 subjects, or 25% of the total) or revealed only diverse aerobic germs (in 10 subjects, or 50% of the total), the germs more frequently found being: negative coagulase staphylococcus albus (in 7 subjects, or 35% of the total), alpha hemolytic streptococcus (in 4 subjects, or 20% of the total) and Neisseria catarrhalis (in 4 subjects, or 20% of the total). In 5 (25%) of the 20 subjects, coliform bacteria were found in the upper small bowel (Klebsiella pneumonia in 2, and Escherichia coli in the remaining 3). Of those 5 subjects, only 2 (10% or the total of 20) had the microorganisms exclusively in the bowel, and in both the concentration of germs was 10(4)/ml. On the contrary, the 3 remaining subjects (15% of the total) had coliforms also in the pharynx; in 2 of the 3 subjects the concentration of germs found in the bowel was 10(3)/ml, and, in the remaining one, 10/ml; only one of the 3 subjects presented germs in the pharynx in a greater concentration than in the bowel, while another presented germs in the same concentration in both localizations, and the remaining one presented germs in the bowel in a concentration lower than in the pharynx.(ABSTRACT TRUNCATED AT 250 WORDS)