The paper presents a performance assessment method whose purpose is to make controller maintenance based on adjusting the controller gain, more systematic. A normalized gradient of a quadratic cost function is calculated with regard to the loop gain. It is shown that this statistic is very easy to calculate and that the information can be useful to improve performance. Calculations of the gradient for two loops from a pulp and paper mill that had performance problems show the validity of the method in an industrial setting. (C) 2006 Elsevier Ltd. All rights reserved.