An optimisation procedure based on genetic algorithm approach is developed for the determination of substrate feed profiles for the optimal operation of fed-batch bioreactors. The problem specific knowledge generated through the rigorous application of the optimal control theory is used to formulate the set of decision variables representing the qualitative and quantitative aspects of the feed rate profile. A customized genetic algorithm with suitable genetic operators is used for generating the optimal feed profiles. Even though the optimal control theory is not explicitly used, the feed rate policies thus evolved are shown to retain the characteristics of the profiles generated through the application of optimal control theory. The efficiency of the proposed algorithm is demonstrated with two fermentation processes: secreted protein and yeast cell mass production. (C) 2003 Elsevier Science Ltd. All rights reserved.