The genotoxicity of four vanadium compounds, sodium metavanadate (NaVO3), ammonium meta-vanadate (NH4VO3), sodium ortovanadate (Na3VO4) and vanadyl sulfate (SVO5), was evaluated in human lymphocyte cultures using structural and numerical chromosome aberrations, micronuclei, sister-chromatid exchanges and satellite chromosome associations as endpoints. These compounds were not found to increase the frequency of structural chromosome aberrations whereas a significant increase in numerical aberrations, micronuclei and satellite associations was found. Since these results could have been related to a possible mechanism of the action of vanadium as a mitotic spindle poison, the fluorescence in situ hybridization (FISH) technique was applied to the human lymphocyte micronucleus assay, by means of an alphoid centromere-specific DNA probe. The four vanadium salts showed a micronucleus percentage with positive signal (presence of centromere and thus of whole chromosome(s)) that was always higher than 68% at all doses tested. That confirmed the aneuploidogenic potentiality of vanadium.