Exposure of human alimentation-destined animals to toxic substances can be an important risk factor for human health. Mutagenicity tests represent a good method for genotoxic effect evaluation of environmental pollutants. The micronucleus frequency in peripheral blood and bone marrow erythrocytes has been evaluated in four domestic Ungulate species (ox, sheep, swine and horse). For each species two or three groups of animals coming from Italy and other European countries were analysed and the results indicate a relatively low mean frequency of micronucleated erythrocytes (ME), both in peripheral blood and bone marrow. The comparison between these two frequencies in the four species studied shows that the ME frequency in sheep and horse is significantly higher in peripheral blood than in bone marrow, whereas in bovines it is higher in the bone marrow, and in swine the difference is not significant. These results could indicate that in ox and swine the spleen is involved in ME removal from the peripheral circulation, as is known for other species including man. Nevertheless, it cannot be excluded that the same occurs in the other two species, since they exhibit a relatively low peripheral blood ME frequency as well. Further studies on domestic mammals are needed to clarify the spleen function and verify the use of the peripheral blood micronucleus test for genotoxic biomonitoring. At present, the application of the micronucleus test to the bone marrow seems a more suitable method, but, being invasive, it can be used only as a control system of animal hygiene and health, in addition to the routine tests, rather than for biomonitoring.