When the maintenance of expert systems incorporates not only knowledge bases but also inference engines, algorithms, and user interface modules, the maintenance of the expert systems needs to adopt software maintenance methodologies such as software reuse. We have developed a regenerative expert system approach (REGENESYS) that can modify the rules and program modules of a standard expert system according to the changed specification. We have also proposed a procedure for the approach and illustrated it with the scheduling expert systems for shipbuilding. By adopting the regenerative expert system approach, we can reduce the burden of developing systems for rare occurrences and maintain the capability of modular modification. (C) 1998 Elsevier Science Ltd. All rights reserved.