Lactobacillus sp. are important inhabitants of the intestines of animals. They are also largely used as probiotics for both humans and animals. To exert beneficial effects, lactobacilli have to survive through the gastrointestinal transit. Based on bile-salt resistance, pH tolerance, antimicrobial activity and heat resistance, Lactobacillus plantarum 4.1 and Lactobacillus reuteri 3S7 were previously selected and used as probiotic additives in pelleted feeding trials. Both strains were fed to pigs (sows and piglets) at a cell number of ca. 10(10) viable cells per day. A polyphasic approach, comprising growth on selective media, Biolog System analysis, 16S rRNA gene sequencing and RAPD-PCR typing, was used to identify and differentiate L. plantarum 4.1 and L. reuteri 3S7 from other faecal Lactobacillus sp., L. plantarum 4.1 and L. reuteri 3S7 had the capacity to survive during the gastrointestinal transit and were found in the feaces at a cell number of 6-8 log cfu/g. Their persistence was shown after 6 days from the administration. Compared to untreated pigs, the administration of L. plantarum 4.1 and L. reuteri 3S7 significantly (P<0.05) decreased the population of Enterobacteriaceae. Besides, the beta-glucuronidase activity of all pigs decreased of ca. 23.0% during administration. The findings of this study showed that L. plantarum 4.1 and L. reuteri 3S7 have the potential to be used as probiotic additives in pelleted feed for pigs.