In this study, a fuzzy logic controller is developed using a new methodology for designing its rule-base. This controller consists of two rule-base blocks and a logical switch in between. The rule-base blocks admit two inputs one of which is newly devised and called ''normalized acceleration'' and the other one is the classical ''error''. The newly devised input is derived using the first and the second order derivatives of the error and it gives a relative value about the ''fastness'' or ''slowness'' of the system response. A comparative performance analysis has been made through the simulation results of the MacVicar-Whelan controller and the proposed fuzzy logic controller on a marginally stable system. The robustness and effectiveness of the new fuzzy logic controller over the typical MacVicar-Whelan controller has also been illustrated by simulations done on a system under various disturbances and time delays. (C) 2002 Elsevier Science Ltd. All rights reserved.