The clastogenic activity of the herbicide maleic hydrazide (MH) in Vicia faba seedlings grown in different soils was studied. In the first series of experiments the seedlings were treated with MH in nine soils of different selected properties. The second experimental protocol provided for a growth step in each of the nine soils under study and then for the treatment of the seedlings with MH in a sandy soil. The results obtained show that less clastogenic damage (induction of micronuclei and aberrant anatelophases) was observed in the seedlings treated in the soils with a high content of organic and clay-type colloids. A growth step carried out in the organic soils, before the treatment with MH, was observed to reduce the genotoxic effects of the herbicide when the seedlings were treated in a sandy soil. These findings suggest that some components of soil organic matter, such as fulvic and humic acids, may be absorbed by the plant roots and so carry out an antimutagenic activity against MH within the plant.