Methods and tools that support systems development (SD) are usually motivated by a promise of better quality or increased productivity. In large software organizations specialised methods departments often manage these methods and tools. However these methods departments often focus more on purchase, tailoring and maintenance of technologies rather than on systematically diffusing methods and tools into current practices. This paper reports from a systematic improvement initiative in a large software organization. The aim of this effort was to diagnose diffusion practices, evaluate and adapt a service that can improve diffusion practices, and to diffuse this new service. Insights from this initiativet together with theoretical reflections on diffusion of SD technologies are provided. It is suggested that provision of services that help projects understand and plan diffusion of new SD technologies can play a key role in developing the focus and competencies needed to improve diffusion practices in large software organizations.