In contrast to beta-testing, formal verification can guarantee correctness of a program against a specification. Two basic verification techniques are theorem proving and model checking. Both have strengths and weaknesses. Theorem proving is powerful, but difficult to use for a software engineer. Model checking is fully automatic, but less powerful and hard to extend. This paper shows a possibility, how to combine both approaches, in order to surround the weaknesses. Concretely, we automatize the proof of while loops in the theorem prover KeY, by using the model checker BLAST.