Technical Abstract: Campylobacter is one of the leading causes of food-borne illness in the United States, and epidemiological evidence indicates poultry and poultry products to be a significant source of human Campylobacter infections. Caprylic acid, an 8-carbon medium chain fatty acid, can reduce Campylobacter colonization in chickens. How caprylic acid reduces Campylobacter carriage may be related to changes in intestinal microflora. To evaluate this possibility, cecal microbial populations were evaluated using denaturing gradient gel electrophoresis (DGGE) in market age broiler chickens fed caprylic acid. In the first trial, day of hatch chicks (n=40 per trial) were assigned to four treatment groups (n=10 birds per treatment group): positive controls (Campylobacter, no caprylic acid), 0.7% caprylic acid supplemented in feed for the last 3 days of the trial, or treatments with a 12 h feed withdrawal before slaughter. Treatments were similar for Trial 2, except caprylic acid was supplemented for the last 7 days of the trial. On day 14 of age, chicks were orally challenged with C. jejuni, and on day 42, ceca were collected for DGGE and Campylobacter analysis. Caprylic acid supplemented for 3 or 7 days at 0.7% reduced Campylobacter compared to the positive controls, except for the 7-day treatment with a 12 h feed withdrawal period. DGGE profiles of the cecal content showed very limited differences in microbial populations. The results of this study indicate that caprylic acid's ability to reduce Campylobacter does not appear to be due to changes in cecal microflora.