Regression testing can be systematically applied at the software architecture level in order to reduce the cost of retesting modified systems, and also to assess the regression testability of the evolved system. With the advent of model-based specification and analysis of software architectures, regression testing at the architectural level can be handled by analyzing how the architectural model evolves when moving from an initial to a subsequent version. This paper analyzes how model differencing, a recent research topic in the model-based community, can be employed for implementing model-based architecture-level regression testing.