Today's consumers can select functional foods from a wide variety of these products with components such as proteins, carotenes, dietary fiber or microorganisms known as "probiotics", among which are those belonging to the Lactobacillus and Bifidobacteri umgenera. This work evaluates the effect of the addition of ascorbic acid and Lcysteine as redox potential reducing agents (Eh) on the propagation of a probiotic microorganism, Lactobacillus casei, in milk. The reducing agents were added to milk individually or combined in concentrations of 0, 100 and 200 ppm, in order to obtain the combination that would allow the maximum growth of the probiotic culture. The different combinations of ascorbic acid and L-cysteine were evaluated on the number of colony forming units of L. casei before and after 5 days of milk incubation. The propagation of the microorganism was analyzed by counting colonies on Mann Rogosa Sharp (MRS) agar plates incubated anaerobically at 35 ± 1°C for 72 h. The combination of the higher concentration of ascorbic acid (200 ppm) and L-cysteine (100 or 200 ppm) gave the maximum count of L. casei, with a population higher than 1010 CFU/mL. These additives proved to be effective in the multiplication of the probiotic bacteria to generate new healthy products in the food industry.