Agent-orientation has gained increased importance in recent years with the emergence and growth of the World Wide Web, both as an area of study in itself and as a component of other disciplines such as software engineering. As a result, this has led to an increased amount of research developing new informal and formal software engineering techniques to support agent-oriented system specification, design, validation and development. In this paper, we present a formal notation called AgentZ that combines the model concepts and structure proposed by TAO (Taming Agents and Objects), a conceptual framework that provides conceptual foundations for agents and objects, with the well known Z and Object-Z formal representation languages. AgentZ was built to provide a formal notation that allows the verification of design models, a key issue within the emerging agent-oriented software engineering research and, as a result, it can help to improve the quality of MAS.