Crepis capillaris (2n=6) is an excellent plant for the assay of chromosome aberrations after mutagenic treatment. It has simple karyotype: three pairs of morphologically distinct and relatively large chromosomes. The frequency of structural chromosome aberrations and micronuclei in root meristem cells has been used for evaluation of the genotoxicity of chemicals and environmental pollutants. The introduction of fluorescence in situ hybridization method allows more detailed detection and localization of chromosomal rearrangements not only in mitotic but also in interphase nuclei. We demonstrate a few examples of the detection of chromosomal aberrations using rDNA and telomeric sequences as probes for in situ hybridization to C. capillaris chromosomes.