Carbon monoxide (CO) is a highly poisonous, odorless, colorless, tasteless, flammable gas used as a reducing chemical in metallurgical operations, in organic synthesis of petroleum-type products, and in the manufacture of metal carbonyls. The threshold limit value adopted for CO for the human is 25 ppm; its toxic activity is via anoxia to the cardiovascular, central nervous and reproductive systems. Developmental neurotoxicity is the primary manifestation of the effects of CO in the human. The characteristic responses indicate that developmental toxicity in the form of embryolethality, growth retardation, and postnatal functional impairment is commonly induced in laboratory animals from CO exposures and, rarely, malformation is induced, only in the rat and guinea pig. A number of useful reviews on carbon-monoxide-induced developmental toxicity are available.