Established anti-mitotic drugs such as vinca alkaloids, taxanes, or epothilones activate the SAC either by destabilizing or stabilizing spindle microtubules resulting in mitotic arrest. Prolonged arrest in mitosis forces a cell either into a mitotic exit without cytokinesis or into a mitotic catastrophe leading to cell death. In contrast, Mps1 inhibitors inactivate the SAC and accelerate progression of cells through mitosis eventually resulting in severe chromosomal missegregation, mitotic catastrophe, and cell death. Consequently, Mps1 inhibition leads to failure of cells to arrest in mitosis in response to anti-mitotic drugs. Thus, the combination of microtubule-interfering agents and Mps1 inhibition strongly increases chromosomal segregation errors and cell death and therefore, constitutes an efficient strategy for selectively eliminating tumor cells.