Clastogenicity of tritiated thymidine to the mouse bone marrow.

Tritiated thymidine (3HTdR; 120 microCi/mouse) increases the incidence of micronucleated polychromatic erythrocytes (MPE) in bone marrow PE of both B6CF1 and CBA male mice. This effect observed in vivo reflects, the clastogenicity reported by other investigators for 3HTdR in vitro. Thymidine itself was concluded to be inactive in the assay at a dose-level 100 times greater than that required to show activity for 3HTdR. These observations are of relevance to those employing 3HTdR to monitor the mitogenic activity and the genotoxicity of chemicals.