The introduction of UML models in the software life cycle poses new issues and challenges that are not adequately supported by current state-of-the-art development tools, especially concerning V&V activities. Indeed, every tool usually focuses on a small set of specialized activities, failing to provide a satisfactory (general purpose) V&V framework. In this paper we propose a methodology which allows a seamless integration of V&V into a UML-based development environment. The methodology exploits a set of supporting tools designed to be integrated in a unified framework. We believe that such proactive collaboration between tools can reduce significantly both effort and time required to tackle consistency, correctness, quality and long-term maintainability of UML models, increasing the development productivity and the overall quality of the delivered system.