Different concentrations of corn steep liquor (CSL) were tested in the cultivation of Zymomonas mobilis, Cell growth, ethanol production, and the formation of glucose-fructose oxidoreductase (GFOR) and glucono-delta -lactonase (GL), the enzymes responsible for the bio-production of gluconic acid and sorbitol, were examined. The cell yields using 25 g CSL l(-1) and 40 g CSL l(-1) (Y(X/S)approximate to0.031 g g(-1)) were close to that obtained with 5 g yeast extract (YE) l(-1). With 5 g CSL l(-1) and 15 g CSL l(-1), the nutritional limitation led to smaller Y-X/S Using 100 g CSL l(-1) produced an inhibitory effect on cell growth. Similar ethanol yields (92-95%) were calculated for each concentration of CSL and also for YE medium. The highest specific GFOR/GL activities (13.2-13.5 U g-l dry cell) were reached with 25 g CSL l(-1) and 40 g CSL l(-1), values comparable to that achieved with 5 g YE l(-1). The results confirm that CSL is an effective and cheap supplement fur Z. mobilis medium, increasing the economic potential of a large-scale bio-production of sorbitol and gluconic acid by untreated Z. mobilis cells. The economic feasibility of the process is discussed.