The purpose of the project was to determine the feasibility of using human-derived antibodies against the chromosomal kinetochore region coupled with immunofluorescence staining as a method for evaluating the induction of aneuploidy in mammalian cells in vitro and in vivo. The technique was applied to (1) Chinese hamster cells (V79 cells), human fibroblasts, and peripheral lymphocytes interphase cells in vitro; (2) mouse bone marrow cells in vivo; and (3) mature human and rat sperm. Although kinetochore staining can be accomplished on a routine basis on mammalian interphase in vitro and in vivo cells, the technique does not appear to offer the staining intensity and/or persistence to allow for an accurate enumeration of the total genomic complement of a Chinese hamster, mouse or human cell. It was found that kinetochore structures are not visible in nature before or after techniques to cause sperm head enlargement. Kinetochore structures can, most likely, be detected in micronuclei.