AbstractApproximately 1.5 million workers in the United States are exposed to arsenic. Occupational exposure is primarily by inhalation. NIOSH recommends that time‐integrated exposure to arsenic in air not exceed 2 μ.g/m3. Recent exposure is accurately measured by urine assay; urine arsenic concentrations above 50 μg/liter indicate increased absorption. Hair assay is a semiquantitative index of past exposure. Toxicity is associated primarily with the trivalent (3 + ) form of arsenic. Acute poisoning is caused most commonly by contaminated food or drink; it is rarely occupational. Chronic intoxication is characterized by dermatitis, hyper‐pigmentation, keratoses, peripheral neuropathy (primarily sensory), irritation of the upper and lower respiratory tract, and occasionally by hepatic toxicity and peripheral vasculopathy (blackfoot disease). Arsenic is not carcinogenic in animal species, but is mutagenic in Syrian hamster cells. In man, arsenic is known definitely to cause cancer of skin, lung, and liver (angiosarcoma) and possibly to cause lym