The correlation between changes of microflora and levels of volatile fatty acids (VFA) in the ceca of chickens infected with Eimeria tenella and Salmonella typhimurium was studied. Four groups consisted of uninfected controls, inoculated with 40, 000 E. tenella oocysts, inoculated with a daily dose of approximately 104 S. typhimurium for 5 consecutive days, and inoculated with a combination of both organisms. Seven, 10 and 14 days after coccidial inoculation, microflora and VFA levels in the cecal contents were examined. In the ceca of E. tenella-infected groups, decreases in the polulations of Bacteroides spp., Bifidobacterium spp. and Lactobacillus spp., and increases in the populations of Enterobacteriaceae, including S. typhimurium, and Clostridium perfringens were observed. VFA levels in the E. tenella-infected ceca were significantly lower than those in uninfected ones. There were low correlation coefficients between microorganism populations and VFA levels.