Aims: Lactobacilli are known to produce acids from sucrose or glucose. This acid production can cause a drop in pH which is sufficiently significant to demineralize the hard tissues of the teeth. Some authors have demonstrated the benefits of substituting sorbitol or xylitol for sucrose, The aim of this work was to study the acid production of salivary lactobacilli with one test sugar (glucose) and two polyols (sorbitol and xylitol). Methods and Results: The pH-lowering potential of three strains of oral lactobacilli was recorded with glucose or one of the polyols at three different concentrations. The results showed that polyols were broken down by certain strains of lactobacilli. When this degradation took place, the pH dropped to values sufficiently low to demineralize the hard tissues of the teeth. Conclusions: Further studies must be carried out on the metabolism of polyols before encouraging their widespread substitution for sucrose.