Publisher Summary This chapter describes a general isolation procedure that is rapid and applicable to the isolation of chromosomes, mitotic apparatus, or nuclei. The methods employed for the mass isolation of any cell organelle are limited by the physical and chemical nature of the structure, tile adherence of contaminating materials from the cell, and the final desired state of the isolated component. Isolation of subcellular components for experimental study has generally been specific for the cell organelle desired, with little or no regard to the slight modifications, which might allow nearly identical isolation conditions for a number of cellularly and functionally related structures. Chromosomes, mitotic apparatus, and nuclei are all stable in the chromosome isolation buffer, but it is found that for Chinese hamster cells, slight modifications made in the buffer system for mitotic apparatus and for nuclei augmented cell breakage and decreased the amount of contamination of the product. The common nuclei isolation methods use either aqueous or nonaqueous homogenization media, the choice of which depends upon the nature of the end products desired. The nonaqueous organic solvent techniques unavoidably damage the nuclear membrane, whereas the aqueous methods allow a leakage of soluble nuclear components.