Eugenol, a widely used chemical in clinical dentistry, was evaluated for genotoxicity using the bone marrow micronucleus (Mn) assay in mice. Three doses (100, 400 or 600 mg/kg) were administered intraperitoneally (i.p.). The animals were killed 30 h post-treatment and the frequency of Mn in 1000 polychromatic erythrocytes (PCE) was determined. Corn oil and methyl methanesulfonate (MMS) were used as negative and positive controls, respectively. Only 400 and 600 mg/kg doses showed significant induction of Mn. We also studied the effect of eugenol at different recovery times (24, 30 or 48 h) with a dose of 400 mg/kg. A positive Mn response was seen at all three post-treatment times, but the differences between them were not significant. For treatment and control groups, the cytotoxicity was in the normal range, measured as the ratio of PCE/NCE (normochromatic erythrocytes).