This paper presents a new PID controller design method for integrating processes with time delay and time constant. First, the conditions that guarantee the stability of closed-loop system are investigated. Then an optimization method using H∞ performance criterion is developed for deriving the controller. The stability and performance of closed-loop system are analyzed. The relationship between the closed-loop frequency response and the corresponding time-domain response is also examined. Examples are given to illustrate the proposed method. (1999 Elsevier Science Ltd. All rights reserved.