A human interferon beta expressed from a synthetic gene was produced in high cell density culture by recombinant Escherichia coli using an optimized linear feeding strategy. The optimal induction conditions to be determined consisted of inducer concentration and dry cell weight at the time of induction. For this purpose, the response surface methodology was applied. Under optimal conditions, the maximum interferon beta concentration and overall productivity of 2.2 g/l and 0.151 g/lh were obtained, respectively, as the highest amounts ever reported for this protein. Two optimal ranges of dry cell weight and IPTG concentration consisting of 50 g/l and 2.54 mM, and 70 g/l and 1.29 mM were predicted, respectively, at which maximum productivity was achieved. By using a novel feeding strategy with linear variation of specific growth rate during high cell density fermentation, the maximum biomass productivity of 5.037g/lh was obtained in a defined medium during 16h. Then, by applying the optimum induction conditions, we accomplished an increase in overall productivity by more than three-fold over the central point. This is the first report showing the high production of human interferon beta by a synthetic gene in a simple fed-batch high cell density culture of recombinant E coli in a defined medium. (c) 2008 Elsevier Ltd. All rights reserved.