Cytogenetic investigations were carried out on 50 workers exposed to stone dust in a stone crusher industry and on 25 control subjects never exposed to such dust. The frequency of chromosomal aberrations and sister chromatid exchanges in exposed individuals was significantly higher than that in controls (P less than 0.01). The cytogenetic indices demonstrated a clear dependence on the working environment. The effect of smoking and/or alcoholic habits coupled with exposure to stone dust has also been investigated. The results indicate that the mutagenic risk in the working environment is probably associated with silica dust in the area.