An evaluation of the risks to human health and the environment posed by exposure to carbon monoxide, a colourless, flammable gas produced by both natural and anthropogenic processes. Although studies of carbon monoxide poisoning are included, the report gives major attention to possible health risks linked to the relatively low concentrations that characterize most exposures. It also aims to identify sub-populations that may be particularly susceptible to adverse health effects. Close to 1000 references are included in the assessment. There are chapters covering the following issues: environmental distribution and transformation; sources of personal exposure; toxicokinetics and mechanisms of action; and health effects in humans, with investigations of adverse effects linked to typical ambient exposure levels. Among its many conclusions, the report calls for better education of the general population about the risks of exposure, particularly in individuals with cardiovascular and respiratory disease, and better awareness among medical professions of the dangers of carbon monoxide exposure during pregnancy.