The frequency of chromosome aberrations from bone marrow cells of 50 specimens of the common vole (Microtus arvalis) was examined in the years 1981 and 1982. The animals were captured in the regions exposed to various degrees of industrial and agricultural pollution. Chromatid and chromosome breaks and fragments were found in the cells of the animals studied. The overall average frequency was 1.12 aberrations per 100 cells. No significant differences were found between samples from various localities and regions. The ascertained aberration frequency probably represents the spontaneous level.