Don Chinese-hamster cells were treated with 25, 50, or 75 micrograms/milliliter (microg/ml) of sodium-fluoride (7681494) to determine the chromosomal effects of fluoride exposure on these cells. Cultures were assayed at 12, 24, and 36 hours after initiation of treatment. Chromosomal aberrations were recorded for all the concentrations used. Maximum effect at all concentrations was observed after 24 hours of treatment. Several kinds of abnormalities were revealed with the main ones being bridges, double bridges, sidearm bridges, bridges with fragments, tripolar and multipolar anaphases with and without bridges, fragments, and laggards. “Y” and “X” configurations were also noted at metaphase. No significant differences were noted for different concentrations of sodium-fluoride, while the difference between treated and control cultures was significant at the 5 percent probability level. The authors suggest that bridges scored in anaphase/telophase may result from stickiness of chromosomes or from exchanges between chromosomes or chromatids. Fluoride may be responsible for disruption of microtubules causing “Y” and “X” type configurations to occur in metaphase, since sodium-fluoride affects the rate of protein synthesis and since the mitotic spindle fibers are composed of proteins. The authors conclude that sodium-fluoride may be considered to be clastogenic in these cells.