The biomonitoring of genotoxic effects in environmental complex mixtures using higher plants is very useful for hazard evaluation. In this study we evaluated the potential application of plant genotoxicity tests in monitoring mutagens in landfill environment. The clastogenic effects of gaseous emissions (biogas)from three municipal landfills were evaluated by in situ monitoring using the Tradescantia micronucleus assay. The cytotoxicity and genotoxicity of leachates were studied using the Allium cepa test. We found no significant differences in micronuclei frequency in pollen cells of Tradescantia. Leachate samples showed elevated toxicity that inhibited root tip development in Allium cepa. Genotoxicity of the leachates was evaluated in diluted samples only. We found a significant increase in chromosomal metaphase aberrations only in one of the samples analyzed. In conclusion, biogas was not shown to be a real hazard, whereas leachates were found to display elevated toxicity. It would be advisable to treat leachates before releasing them into the environment as they can cause ecological damages. Since plant bioassays are very useful for the in situ monitoring of environmental genotoxins they are important for the prevention of environmental pollution resulting from the disposal of solid waste.