The authors report and evaluate the experience of applying object-oriented techniques to the development of a real-time system for monitoring and control of remote sites. The system which is currently installed at several sites in the UK and elsewhere in Europe also includes database management functions and an interactive operator interface. The authors focus on the object-oriented aspects of the system architecture and on the development process model. Together they provide a technical and organisational framework for projects of similar nature. The pros and cons of the solutions adopted are discussed.