Lactobacillus fermentum CECT5716, a probiotic strain isolated from human milk, was characterized in a previous study. The objective of this study was to evaluate its sensitivity to antibiotics and its potential toxicity and translocation ability after oral administration to mice. For this purpose, 40 Balb/C mice were divided in two groups (n=20 per group). One group was treated orally with 10(10) colony forming units (cfu)/mouse/day of Lb. fermentum CECT5716 during 28 d. The other group only received the excipient and was used as control. Food intake, body weight, bacterial translocation and different biochemical and haematological parameters were analysed. Oral administration of Lb. fermentum CECT5716 to mice had no adverse effects on mice. There were no significant differences in body weight or food intake between control and probiotic-treated mice. No bacteraemia was observed and there was no treatment-associated bacterial translocation to liver or spleen. Stress oxidative markers were not different in control and probiotic-treated mice. These results suggest that the strain Lb. fermentum CECT5716 is non-pathogenic for mice even in doses 10,000 times higher (expressed per kg of body weight) than those normally consumed by humans.