Unit testing aims to ensure that methods correctly implement the specified and implied pre- and post-conditions, while integration testing ensures that modules correctly follow interaction protocols. While the generation of unit test cases has been explored extensively in the literature, there is still little work on the generation of integration test cases. In this paper we present a new technique to generate integration test cases that leverages existing unit test cases. Our key observation is that both, unit and integration testing, use method calls as the atoms to construct test cases from. Unit tests contain information on how to instantiate classes in meaningful ways, how to construct arguments for method calls, and what the resulting system state should be after calling methods with those arguments. We use this information to construct more complex test cases that focus on class interactions rather than on individual state transformations caused by single method calls. This paper presents the approach and shows that the generated test cases can find interesting faults, compared to test suites generated with state of the art approaches.