The escape of individual interphase chromosomes from nuclei of reversibly permeabilized Chinese hamster ovary (CHO) cells was utilized for the visualization of condensing interphase chromosomes in a cell cycle-dependent manner in synchronized cells. Major interphase chromosomal forms include: (a) mid-S-phase globular chromosomes at 3.0 C-value, (b) late mid-S-phase fibrous hemicircular forms (3.3 C), (c) late-S-phase supercoiled ribbons (3.7 C), and (d) end-S-phase elongated, bent prechromosomal structures (4.0 C).