This paper gathers data on the most current aspects of arsenic action, especially its influence on the cardiovascular system, blood and bone marrow. A potential carcinogenic mechanism of arsenic is also discussed. Arsenic is a potent toxicant that may exist in several valencies and in a number of inorganic and organic forms. Most cases of arsenic-induced toxicity in humans are due to exposure to inorganic arsenic, and there is an extensive database on the human health effects of common arsenic oxides and oxyacids. Exposure of humans living near hazardous waste sites may involve inhalation of arsenic dusts in the air, ingestion of arsenic in water, food or soil, or dermal contact with contaminated soil or water. The exposure to arsenic via the inhalation route is responsible for the increased risk of lung cancer, although respiratory irritation, nausea and skin effects may also occur. The oral route of exposure to arsenic predominates in the general population. The most common effects of arsenic ingestion are gastrointestinal irritation, peripheral neuropathy, vascular lesions, anemia, skin diseases, including skin cancer and other cancers of the internal organs like bladder, kidney, liver or lung. Relatively little information is available on the effects of direct dermal contact with inorganic arsenicals, but several studies indicate local irritation and dermatitis as the major ones.