Arsenic is widely distributed in nature and mainly transported in the envi ronment by water. All humans are exposed to low levels of arsenic through air, drinking-water, food and beverages. Cigarette smokers may be exposed to arsenic in tobacco, but the chemical form of arsenic in the smoke remains unclear. For most people, food constitutes the largest source of arsenic intake, with smaller amounts from drinking-water and air. Some edible fish, shellfish and seaweed contain elevated levels of arsenic, but this is predomi nately in an organic form that has low toxicity. Above-average levels of arsenic exposure through ingestion have usually been observed among people who live in areas where drinking-water has an elevated level of inorganic arsenic because of natural mineral deposits or contaminations from human activities; among patients treated with drugs containing inorganic arsenic for leukemia, psoriasis and chronic bronchial asthma; and among vintners who consume arsenic-contaminated grape wine. Workers involved in the processing of copper, gold and lead ores; in the use of arsenic as pigments and dyes; in the production and use of agricultural pesticides; in the manufacturing of glass and various pharmaceutical substances; and in the chimney sweeping business also have a high exposure to arsenic (World Health Organization, 1981; US Public Health Service, 1989). Most ingested and inhaled arsenic is well absorbed through the gastro-intestinal tract and lung into the bloodstream. It is distributed in a large number of organs including the lungs, liver, kidneys and skin (Hunter et ai,1942). Most arsenic absorbed in the body is converted by the liver to less toxic methylated forms that are efficiently excreted in the urine (Vahter and Marafante, 1983; Vahter et al,1984).