For most plant species growing in polluted areas genotoxicity assays are not available. We have studied the possibility of using the alkaline protocol of the Comet assay as a method for detecting induced DNA damage in a grass Calamagrostis epigejos, growing wild in highly polluted areas. To calibrate the Comet assay for C. epigejos, two model mutagens were applied: the monofunctional alkylating agent ethyl methanesulfonate (EMS) and gamma-rays. With increasing concentrations of EMS (0 to 10 mM, 18 h treatment at 26 degrees C) applied on excised leaves, the DNA damage, as expressed by the tail moment (TM) values, increased from 4.7 +/- 0.9 to 60.8 +/- 2.7 microns. After gamma irradiation (0 to 30 Gy) the TM value increased from 4.2 +/- 0.2 to 48.1 +/- 1.7 microns. A 24 to 72 h recovery of leaves after EMS treatment in an EMS-free medium did not result in a significant change in the induced EMS damage. By contrast, a 24 h recovery after gamma-irradiation led to a complete repair of DNA damage measurable by the Comet assay. We have measured the DNA damage in nuclei of leaves of C. epigejos plants growing in the area of a sediment reservoir with substrates from uranium mining, where the ore was exploited through leaching with sulfuric acid. The average specific activity of natural radionuclides measured in the substrate was for 226Ra = 11,818 Bq kg-1, for 232Th = 66 Bq kg-1 and for 40K = 75 Bq kg-1. No significant increase in the DNA damage in plants growing on the sediment substrate above the DNA damage in control plants was detected by the Comet assay.