This book evaluates the risks that cyanides present to human health. Although many chemical forms of cyanide are used in industrial applications or are present in the environment, the primary toxic agent, regardless of their origin, is the cyanide anion Cyanides are characterized by their high acute toxicity by all routes of administration. This toxicity is believed to result from inactivation of cytochrome oxidase and inhibition of cellular respiration, producing consequent histotoxic anoxia. Cyanides comprise a wide range of compounds of different, chemical complexity, all of which contain the CN moiety. Cyanides are widely used in industry, and hydrogen cyanide gas is also used as a fumigant. The principal natural sources of cyanides are plants (more than 2000 species), including fruits and vegetables, that contain cyanogenic glycosides, whose hydrolysis upon ingestion can release cyanide anion. Of these plants, cassava (tapioca, manioc) and sorghum are staple foods for hundreds of millions of people in many tropical countries. The natural biogenic processes of higher plants, bacteria, and fungi release hydrogen cyanide into the atmosphere. The majority of the population is exposed to very low levels of cyanide in the general environment. There are, however, specific subgroups whose exposure is potentially higher. These include individuals involved in the large-scale processing of cassava and those consuming significant quantities of improperly prepared foods containing cyanogenic glycosides, including cassava.