Statistically-based experimental designs were applied to optimize a solid-state fermentation for the production Of L-asparaginase by Pseudomonas aeruginosa 50071. Fifteen culture conditions were examined for their significance on enzyme production and specific activity using Plackett-Burman factorial design. pH, casein hydrolysate and corn steep liquor were the most significant factors improving enzyme production process. The second optimization step was to identify optimal values of the three factors that bringing about maximum L-asparaginase activity, using Box-Belinken design. Maximal enzyme activity (142.8 IU) has been detected under the following conditions, pH 7.9; casein hydrolysate, 3.11%; and corn steep liquor, 3.68% which is more than five folds the activity in basal medium. A verification experiment was carried out to examine model validation and revealed more than 99% validity. (C) 2002 Elsevier Science Ltd. All rights reserved.