In the paper, a class of bioprocesses with fully unknown kinetics is considered. Indirect adaptive control algorithm where the process kinetics is presented as unknown time-varying parameter is derived. A general procedure for optimal tuning of kinetic estimator design parameters is proposed by stability analysis of the control scheme. Theoretical results are verified by simulations of the control scheme of continuous fermentation of gluconic acid production by Aspergillus niger. In the conclusion, some other applications of proposed procedure are discussed. (c) 2007 Elsevier Ltd. All rights reserved.