Recombinant Escherichia coli was grown to produce the thermostable Pseudomonas fluorescens lipase by controlling the specific growth rate (mu). At low growth rate (mu = 0.07 h(-1)), a higher cell density (OD600 = 140) was obtained. By calculating the cell yield on nitrogen, the medium was optimized to prevent inhibition of cell growth by nitrogen unbalance. Acetate accumulated in the broth at the same rate as observed in a chemostat under nitrogen-limited fed-batch conditions, but not in a glucose-limited fed-batch culture. Postinduction growth rate affected lipase production more than preinduction growth rate. After induction, more lipase was produced at a low growth rate (mu = 0.1 h(-1)) than at a high growth rate (mu = 0.4 h(-1)). More lipase was produced at 37 than at 20 degrees C at a constant growth rate, indicating that temperature affected other factors in addition to growth rate.