A simple fed-batch process was developed using a modified variable specific growth rate feeding strategy for high cell density cultivation of Escherichia coli BL21 (DE3) expressing human interferon-gamma (hIFN-gamma). The feeding rate was adjusted to achieve the maximum attainable specific growth rate during fed-batch cultivation. In this method, specific growth rate was changed from a maximum value of 0.55 h(-1) at the beginning of feeding and then it was reduced to 0.4 h(-1) at induction time. The final concentration of biomass and IFN-gamma was reached to similar to 115 g l(-1) (DCW) and 42.5 g(hIFN-gamma) l(-1) after 16.5 h, also the final specific yield and overall productivity of recombinant hIFN-gamma (rhIFN-gamma) were obtained 0.37 g(hIFN-gamma) g(-1) DCW and 2.57 g(hIFN-gamma) l(-1) h(-1), respectively. According to available data this is the highest specific yield and productivity that has been reported for recombinant proteins production yet. (c) 2006 Elsevier Ltd. All rights reserved.