Catabolism of l-ascorbate by enteric bacteria is well documented, but no study has formally proved that bacteria of the Lactobacillus genus ferment this compound. However, some genes analogous to those of yiaK-S operon and ula regulon, which encoded proteins leading to l-ascorbate degradation by Escherichia coli and Klebsiella pneumoniae, have been identified in the recently sequenced Lactobacillus rhamnosus GG genome. Investigations by HPLC and in vivo 13C NMR using l-[1,6-13C]-ascorbate showed that L. rhamnosus GG, a common probiotic strain, has the ability to catabolize l-ascorbate under anaerobiosis. The main products of the ascorbate degradation have been identified as CO2, acetate, and lactate. These results are in accordance with the metabolic pathway proposed for the fermentation of l-ascorbate by E. coli