The simultaneous effect of reaction parameters and component concentrations on the microbial lipase from Rhizopus sp. was investigated. The modified simplex optimization method was applied to determine the best operating conditions. The activity measurement was carried out with the pH-stat method where the fatty acids liberated during the enzymic hydrolysis of the olive oil substrate were titrated with NaOH in an automatic tritrimeter Two independent simplex optimizations resulted in a fully converged simplex with respect to all of the parameters. Moreover the converged optimum parameter levels provided the maximum activity, indicating that the global optimum has been found. The maximum activity of 17.9 U/mg was obtained at 40 degrees C, pH 8.3, 41.8 mg/ml gum arabic, and 0.6 mg/ml sodium taurocholate. This response was more than 100% better than a previous one obtained by the ’one-factor-at-a-time’ method.