It is well documented that environmental pollution from industrial activity, sewage farms, hazardous waste sites, incinerators, etc, contributes to the overall cancer risk and that this contribution can be considerable under certain circumstances. It is important, therefore, to identify the level of genotoxic activity in the environment and to relate it to biomarkers of cancer risk in humans. After reviewing a range of cytogenetic assays, we have selected the Tradescantia micronucleus assay (TRAD-MCN) developed by Ma et al to be used in indoor and field evaluations. The meiotic pollen mother cells of T clone 4430 are particularly sensitive to chemical pollutants; the buds are exposed for 6-8 h. We describe assays made down wind from a coal-fired power station and from the vicinity of two waste sites. Statistically significant results were obtained at 200 m and 600 m down wind from the power station; higher levels of micronucleus frequencies (MN) were found in foggy rather than dry conditions. Similarly, in the vicinity of two waste sites the MN frequencies were significantly increased in both dry and foggy conditions up to 1.5 km down wind; this was despite previous efforts to rehabilitate the sites. The TRAD-MCN assay is sensitive, reproducible, easy to perform, well standardized, inexpensive and undemanding in equipment. We propose that it be the primary test for genotoxicity evaluation and mapping followed, in suspicious areas, by human biomarker assays.