All organisms must react to constantly changing surroundings. Environmental factors are thus powerful forces continuously shaping the genomes of all species. Induced genetic changes can be followed using a biomonitor ? a living organism that reacts to a given compound in the environment. A vital but challenging task is identifying organisms with which to study the influence of changing environmental conditions. Plants are especially valuable biomonitors. Here, we describe the use of transgenic plant systems to evaluate the genotoxicity of chemical and radiological compounds. We evaluate the potential of further transgene-based systems for studying somatic and germ-line mutations.