In a continuous two-stage process, the first stage was a three-phase fluidized-bed bioreactor. Using polyurethane foam (PUF) as the cell-immobilization support matrix, the recombinant Eshcherichia coli cells were partially immobilized in the PUF matrix. The free cells were produced by fast regeneration of E. coli cells, and entered the second bioreactor, which was a bubble column, for inducing hEGF expression. By this novel process, each stage could be optimized and hEGF expression was enhanced. The effect of dilution rate on cell growth and hEGF expression was evaluated. The results indicated that the hEGF productivity was proportional to the dilution rate when D < 0.2 h(-1), but decreased when D > 0.2 h(-1). At D = 0.2 h(-1) hEGF productivity reached 31.2 mg(h l)(-1) which was much higher than that in batch process. (C) 2003 Elsevier Ltd. All rights reserved.