In the present study, the effect of Lactobacillus casei subsp. casei and Lactobacillus fermentum inoculation on jejunum and ileum colonization in gnotobiotic piglets has been observed. The characteristic features of the strains used were strong adherence to pig epithelial gut cells as well as inhibitory activity against enteropathogenic E. coli under in vitro conditions. Strains were inoculated to 2, 3, and 4 day old gnotobiotic piglets at a dose of 2 ml (1 x 10(8) germs/ml). On the second day after the last inoculation, Lactobacillus casei subsp. casei strain counts adhered to the jejunum mucosa and those adhered to the ileum mucosa were 4.54 log 10.cm-2 and 5.40 log 10.cm-2, respectively. Lactobacillus fermentum counts adhered to the jejunum mucosa and those adhered to the ileum mucosa were 5.73 log 10.cm-2 and 4.01 log 10.cm-2, respectively. On day 5 after the last inoculation, the counts in both strains were by one log higher. The results obtained point out to the fact that Lactobacillus casei subsp. casei and Lactobacillus fermentum colonized the mucosa of both jejunum and ileum and survived in the intestinal tract. The adherence of lactobacilli to gut cells in vitro correlated with their capability to adhere to the mucosa of both jejunum and ileum in vivo.