This paper describes the four cytogenetic endpoints most frequently used in hazard identification assays as the first step in the risk assessment process. These are structural chromosome aberrations, micronuclei, aneuploidy, and sister chromatid exchanges. The biological mechanisms involved in the formation of the alterations observed in each assay are briefly discussed. Variations in and recent improvements to each assay are described, with an emphasis on the use of molecular techniques to improve the sensitivity of the assay, and to allow for detection of specific alterations that are, or could be, associated with cancer induction. This, in turn, will make the data obtained in the cytogenetic assays more useful in cancer and genetic risk assessment. Thus, the aim of this paper is to encourage cytogeneticists to design their experiments in such a way that the data obtained will be of maximum possible benefit for characterizing and quantifying adverse human health effects, particularly cancer.