Most notable at the site of the Chernobyl nuclear power plant, radioactive contamination has profound effects on the biosphere. Kovalchuk et al. have engineered Arabidopsis thaliana plants to carry a non-functional b-glucuronidase reporter gene that upon radiation induced recombination turn blue (see pp. 1010 and 1054). These plants can be used to monitor to measure the genetic hazard, to plants and animals, of contaminated sites.