The existing standard for object-oriented databases (ODMG) provides no facility for storing behaviour. This lack of stored behaviour introduces problems for generic applications as well as multimedia and federated database systems. Research by others on this issue has resulted in proprietary solutions using non-standard object-oriented database models. This paper discusses types of behaviour in object-oriented database systems, and offers an architecture that implements behaviour on top of an ODMG database. This requires an extension to the standard ODMG metaclass repository to model stored behaviour.