The immunostimulatory effects of Lactobacillus acidophilus LAFTI L10 and Lactobacillus paracasei LAFTI L26 were evaluated to determine their probiotic properties for functional food applications. Mice were given oral doses of either L. acidophilus L10 or L. paracasei L26 (108 CFU/50 microl/day), and the effects on immune responses and bacterial translocation were assessed after the 14-day feeding trial. The proliferative responses of splenocytes to concanavalin A and lipopolysaccharide were significantly higher in mice fed L. acidophilus. Concanavalin A-induced splenocyte proliferative responses increased significantly in mice fed L. paracasei. Interleukin 10 and interferon gamma production from the splenocytes stimulated with concanavalin A were enhanced in mice fed L. acidophilus or L. paracasei. The phagocytic activity of the peritoneal macrophages was significantly higher in mice fed either L. acidophilus or L. paracasei compared with control mice. In mice fed L. acidophilus or L. paracasei, the bacterial translocation of Lactobacillus spp. and total anaerobes to Peyer's patches and mesenteric lymph nodes was modulated compared with that in the control mice. Furthermore, there was no indication of disruption of intestinal mucosal integrity and thus no bacterial translocation to spleen, liver, or blood in mice fed either L. acidophilus or L. paracasei. The results of this study indicate that L. acidophilus and L. paracasei are potential enhancers of systemic immunity and are nonpathogenic, as suggested by their bacterial translocation profiles in healthy mice.