ABSTRACTIn vivo MN test in peripheral erythrocytes of free-living rodents, chronically exposed to heavy metal pollution, was used for detection of genotoxic agents and species at higher risk. Yellow-necked mice (Apodemus flavicollis), Common vole (Microtus arvalis) and Algerian mice (Mus spretus) were collected in areas displaying low or high environmental pollution. Mean frequencies of MN observed in the rodents from the impact region were significantly higher compared to the frequencies from the same species in the background region. The comparative analysis of results confirms, that the Apodemus flavicollis species may be a suitable species for biomonitoring studies using MN frequencies. The results obtained demonstrate that the in vivo MN test may be a sensitive end-point for the detection of genotoxity that may result from the simultaneous action of several metals and may be useful as a biomarker of environmental stress in situ.