To lower the contamination of pork meat with Salmonella, feed additives such as medium chain fatty acids (MCFA's) can be applied at the primary production level. An in vitro continuous culture system, simulating the porcine caecum, was developed for investigating the effect of MCFAs on the pig intestinal microbial community. The system was monitored by plating on selective media, 16S rDNA PCR denaturing gradient gel electrophoresis (PCR-DGGE) and HPLC analysis of fermentation products. In a simulation of the porcine caecum without MCFA treatment, with Salmonella Typhimurium added after stabilization of the microbial community, the strain could establish itself at a stable population size of about 5 log cfu/ml. The effect of selected MCFAs was observed from all monitored parameters and depended on chain length and concentration applied. At a dose of 15 mM, caproate and caprinate did not show any pronounced effect, while a clear Salmonella inhibiting effect (3 log units reduction) was found for caprylate. Doubling the caprylate dose did not result in enhanced Salmonella inhibition.