A chromosome aberration test on bone marrow cells of C57B1/6 mice showed that beta-carotene (BC) applied by oral administration as a E160a food dye (30% oil suspension) at doses of 0.5, 5, and 50 mg/kg simultaneously with cyclophosphamide (CPA) and dioxidine (DN) injected intraperitoneally for a period of 24 h did not modify their clastogenic effects. If the animals were pretreated with perorally administrated beta-carotene dye at doses of 5 and 50 mg/kg (corresponding to 1.5 and 15 mg/kg of BC) for 5 consecutive days, a statistically significant reduction in the clastogenic effect of the DN injected for 24 h but not the CPA was observed. In another set of experiments, E160a and clastogens were administered simultaneously for 5 consecutive days, and the animals were killed 6 h after the last treatment. In this case, BC at the dose of 0.15-15 mg/kg statistically significantly reduced the clastogenicity of DN at all doses used, and of CPA at doses of 1.5 and 15 mg/kg.