The magnitude of the threat to the human genetic material posed by environmental agents has not as yet been fully determined. Never theless, the potential hazards of many chemicals have been identi fied by studies on lower organisms. However, too little is known regarding the comparability or lack of it between the metabolic pathways available in such organisms and those in man. Although at present there is great public concern for what is considered by some as the excessive use of laboratory animals in toxicological testing, it seems clear that the usage of mammalian systems may be deemed...