[Introduction]: The human gastrointestinal tract harbours a complex ecosystem, dominated by anaerobic and facultative anaerobic microorganisms. In particular the lactobacilli have been demonstrated to be dominant in the small intestine with numbers of 102-105 CFU/ml in the ileum, based on culture analysis. Although they belong to one of the dominant inhabitants of the small intestine, lactobacilli form less then 1% of the colon microbiota. Lactobacilli are very interesting because selected strains are claimed to have beneficial effects on the host-organism when ingested; these strains are called probiotics. More attention is necessary to identify the functionality associated with intestinal and probiotic lactobacilli on the intestinal tract and health of the host. The low numbers of lactobacilli in colonic samples, the instability of bacterial mRNA, and the difficulties to obtain small intestinal samples within a certain time scale are strong incentives for investigating these interactions on the more stable protein level. The Lactobacillus plantarum species are quite well recognised for its (potential) probiotic effects in humans. The complete genome for L. plantarum WCFS1 has been published (Kleerebezem et al. 2003). The human model will be a human intestinal epithelial cell. These cell lines are derived from carcinoma and have the ability to grow outside the human body. These cells (cancer cells) have still some features of the original cell type. [Aim]: to study the molecular interactions between lactic acid bacteria and the small intestine.