The general safety of immune-enhancing lactic acid bacteria (LAB) strains Lactobacillus rhamnosus HN001 (DR20), Lb. acidophilus HN017, and Bifidobacterium lactis HN019 (DR10) was investigated in a feeding trial. Groups of BALB/c mice were orally administered test LAB strains or the commercial reference strain Lb. acidophilus LA-1 at 2.5 x 10(9), 5 x 10(10) or 2.5 x 10(12) colony forming units (CFU)/kg body weight/day for 4 weeks. Throughout this time, their feed intake, water intake, and live body weight were monitored. At the end of the 4 week observation period, samples of blood, liver, spleen, kidney, mesenteric lymph nodes, and gut tissues (ileum, caecum, and colon) were collected to determine: haematological parameters (red blood cell and platelet counts, haemoglobin concentration, mean corpuscular volume, mean corpuscular haemoglobin, and mean corpuscular haemoglobin concentration); differential leukocyte counts; blood biochemistry (plasma total protein, albumin, cholesterol, and glucose); mucosal histology (epithelial cell height, mucosal thickness, and villus height); and bacterial translocation to extra-gut tissues (blood, liver, spleen, kidney and mesenteric lymph nodes). DNA finger printing techniques were used to identify any viable bacterial strains recovered from these tissues. The results demonstrated that 4 weeks consumption of these LAB strains had no adverse effects on animals' general health status, haematology, blood biochemistry, gut mucosal histology parameters, or the incidence of bacterial translocation. A few viable LAB cells were recovered from the tissues of animals in both control and test groups, but DNA fingerprinting did not identify any of these as the inoculated strains. The results obtained in this study suggest that the potentially probiotic LAB strains HN001, HN017, and HN019 are non-toxic for mice and are therefore likely to be safe for human use.