Laboratory work aimed at improving the epidemiologic utility of an innovative genotoxicity marker is described. The exfoliated cell micronucleus assay involves microscope analysis of epithelial smears to determine the prevalence of micronucleation, an indicator of structural or numeric chromosomal aberrations. Exfoliated cells are moribund and undergo degenerative phenomena that can produce extranuclear objects difficult to distinguish from classical micronuclei. We also provide evidence that other nuclear anomalies are at least as common as micronucleation and that, therefore, there is the potential for extensive misclassification.