The idea of service-orientation has contributed to an increased interest in Enterprise Architecture (EA) within information systems research and business. One central, yet often underestimated factor of service-orientation is the integration of services. This paper discusses the issue of service integration in the context of Extended Enterprises (EE) from an architectural perspective. Following a design science approach, the design of a Service-Oriented Architecture (SOA) integration platform is aligned with collaboration characteristics in EE. The platform enables the creation of collaborative information and communication technology (ICT) applications built from services, and facilitates the development of shared service repositories in EE contexts. The paper reflects aspects of the architectural design process leading to the platform design. An observational field study allows a qualitative assessment of the resulting service repositories. It suggests that shared service repositories lead to synergy effects within EE contexts.