Pleural mesothelioma, lung cancer, pleural calcification and fibrosis have been observed among inhabitants of the villages in Ivriz-Zanapa valley in Turkey. Earlier reports have stated that these endemic pathological conditions are caused by the inhalation of actinolite asbestos, a mineral commonly used indiscriminately to paint the walls and floors of houses. In the present study, 40 inhabitants in Yassikaya village in Ivriz-Zanapa valley and 20 controls were further investigated. The peripheral blood lymphocytes were cultured and harvested at 72 h for sister chromatid exchange (SCE) frequency. Inhabitants had a raised mean SCE rate compared with a control population.