Chromosome analysis can usually be done with banding cytogenetics or FISH; even though it is way less common, immunohistochemistry on chromosomes is also an important option. That is why this approach was included in this book, which is mainly about FISH approaches. Here, the visualization of centromere proteins (CENP) on chromosomes is described. CENP-B is present on both active and inactive centromeres, while CENP-C is found only on active centromeres. A protocol is presented that allows mitotically active centromeres to be distinguished from inactive ones, which is particularly important in the analysis of dicentric human chromosomes.