Escherichia coli W was cultivated in the pH-stat fed-batch mode in a chemically defined medium containing sucrose as a sole carbon source. A final cell concentration of 105 g/L could be obtained in 36 hrs by feeding 20 g sucrose+0.57 g MgSO47H2O for a definite on-time upon the pH rise. Using the same strategy, a recombinant strain harboring pSYL104 could also be grown to 125 g/L in 48 hrs.