The production of xylitol by microorganisms cultured in media made fr om commercial sugars (xylose with or without other sugars as co-substrates) is reviewed. The microbial strains used for this purpose and the influence of the most important operational variables (including age of inoculum, initial concentrations of cells and substrate, pH, temperature, composition of culture media, dissolved oxygen and product concentration) are considered. The existing information on xylitol production by recombinant microorganisms is summarized.