Arsenic (7440382) exposure was reviewed with regard to occupational burden, toxicity, and studies of arsenic carcinogenicity and mutagenicity. The principal source of occupational exposure has been the removal of arsenic from copper, lead, and zinc ores during smelting operations. Estimates from NIOSH have indicated that 1.5 million workers in the United States are potentially exposed to arsenic on the job. These figures include approximately 660,000 persons with direct exposure potential. Human absorption of arsenic is determined primarily by the measurement of total arsenic concentrations in hair and urine. Urine arsenic levels have been used as indicators of recent exposure whereas hair arsenic levels indicate past arsenic exposure. The toxicity of trivalent arsenic has been shown to be greater than that of pentavalent arsenic. Subacute and chronic toxicities were discussed with regard to dermal, neural, hepatic, cardiovascular, respiratory, and hematopoietic effects. Mutagenic effects attributable to arsenic dosing have been demonstrated in Syrian-hamster cells. Epidemiological studies have indicated a relationship between arsenic exposure and cancers of the skin, liver, and lung and possibly those of lymphatic and hematopoietic tissues, although no animal model for arsenic related cancer induction has been found.