Fed-batch cultures of Escherichia coli W were carried out in a chemically defined medium containing sucrose as a sole carbon source. The substrate feed rate was changed every 30 minutes based on the immediate off-line analysis of medium. When the target specific growth rate was set at 0.15 and 0.2 h(-1), the final cell concentrations of 105 and 110 g dry cell weight/L were obtained in 25 and 20 h, respectively.