The chromosomal passenger complex (CPC) is a key regulator of cell division. Its proper localization during the different phases of mitosis and cytokinesis is crucial for the exertion of its various functions. HDACi treatment has been demonstrated to disturb the centromeric localization of the CPC in tumor cells, thus leading to severe mitotic defects often followed by apoptosis. In this chapter, we describe how HDACi-induced changes of the CPC localization can be analyzed by indirect immunofluorescence using CPC-specific primary and fluorophore-coupled secondary antibodies followed by confocal microscopy.