This review is concerned with the role of chromosomal nonhistone proteins in three important aspects of mitotic events: chromosome condensation, sister chromatid separation at the metaphase:anaphase transition, and interactions between the chromosomes and cytoskeleton that occur during construction of the mitotic spindle and cleavage furrow. Emphasis will be given to the potential roles of topoisomerase II and the chromosome passenger proteins in these events. Other important aspects of mitotic events such as the regulation of the G2-->M transition, the structural changes that affect the nuclear envelope and other organelles during mitosis, and the mechanism of chromosome movement will not be considered here. Despite long histories of often elegant experimentation, all three of our chosen subjects remain areas of lively, ongoing controversy. Thus, although recent advances appear to have taken us many steps closer to an understanding of the underlying mechanisms, we suspect that final answers will be some time in coming.