The effects induced by aneugenic agents on chromosome segregation are manifold. The biological relevance of these effects has led to the development of assays specifically detecting aneugens. In this context, the micronucleus (MN) assay in binucleated human lymphocytes along with FISH has been considered a pertinent tool for detecting aneugenic and clastogenic activity. However, the MN assay is insensitive in detecting aneugenic effects other than chromosome loss. By using the aneugenic model compound colchicine and X chromosome centromere-specific FISH, we have shown that besides chromosome loss in binucleated cells, other effects such as MN in mononucleated cells, cells arrested at metaphase, polyploidy and non-disjunction are also consistently induced by aneugenic agents. A chromosome 1 centromeric probe was used simultaneously with X chromosome centromeric labeling in mononucleated cells in order to distinguish polysomy from polyploidy. It is concluded that all these effects should be considered for a comprehensive evaluation of aneugenic activity.