The oral administration of a 1:20 (wt/vol) dilution of adult turkey cecal contents to poults on the day of hatching protected more than 80% of the poults against challenge at 24 hr of age with approximately 10(3) colony-forming units (CFU) of a nalidixic-acid-resistant strain of Salmonella typhimurium. All untreated poults similarly challenged were colonized. Protection was lost when the challenge dose was 10(6) or greater. When the microflora treatment followed salmonella challenge by 6 hours or more, protection was reduced. If poults were colonized by S. typhimurium, the organisms were found always in the ceca and infrequently in other parts of the intestinal tract. When poults shedding salmonella were mixed with treated poults, more than 70% of the latter remained free of the organism.