A novel optimization procedure has been developed to determine the best combination of variables in large scale fermentation systems. The self-directing optimization or the rotating simplex method of optimization was employed to determine the best suitable combination of parameters, pH (controlled), aeration rate and agitation rate for maximal production of chitinase by Trichoderma harzianum in batch culture. Extracellular enzyme activity increased from an initial value of 0.109 U under unoptimized conditions to a final value of 0.384 U after optimization. A controlled pH of 4.9, an aeration rate of 1.5 l l(-1) per min, and an agitation rate of 224 rpm was found to be the best combination.