The combined effects of initial glucose concentration and inducer (corn oil) concentration on lipase production by freely suspended Rhizopus arrhizus were investigated using response surface methodology (RSM). A 2(2) full-factorial central composite design was employed for experimental design and analysis of the results. The optimum glucose and inducer concentrations were found to be 1.1 and 3.3 g/l, respectively. In these conditions, the biomass concentration of 2.4 g/l with a lipolytic activity of 370 mumol/l min was attained. These results are in close agreement with the model parameters. (C) 2002 Elsevier Science Ltd. All rights reserved.