Lactic acid rod-shaped bacteria stand the effects of osmotic stress in natural living environments as well as in food production process. The complexity of changes occurring in cells as a result of osmotic stress creates the need for extending the knowledge of its effect on the physiological condition of rodshaped Lactobacillus bacteria. The objective of the study was to determine the effect of sodium chloride ranging from 0.5 to 2.5 % on the physiology of cells of Lactobacillus brevis strain isolated from food. A flow cytometry was applied and a fluorescent staining CFDA / PI (carboxyfluorescein diacetate / propidium iodide) was chosen to determine the metabolic activity and integrity of cytoplasmic membranes of cells. Based on the cytometric analysis, four groups were identified of cells with particular parameters: 1: CFDA^–PI⁺; 2: CFDA⁺PI⁺; 3: CFDA^–PI^–; and 4: CFDA⁺PI^–, and their percent content depended on the sodium chloride added to the samples analyzed. In the samples studied, it was found that the content of cells in group 1 increased and in group 4 decreased; this was evidence of the increase in the percent content of cells with damages in cytoplasmic membranes and of the decrease in the percent content of active cells. Based on the plate count results, it was proved that part of the L. brevis population lost culturability in the environment with the highest concentration of sodium chloride: 2.5 %. Furthermore, it was found that the L. brevis strain showed a considerable tolerance to the action of sodium chloride within the range studied and the knowledge in this area might be useful to research the suitability of Lactobacillus strains for industrial processes using screening methods.