Cancer has become the most critical health problem in the United States. It is expected that 25% of the people will develop this dread disease, and many of these will die from the malady. The causes of cancer are varied, but the best estimate available is that 70--90% arise from environmental factors. These statistics have triggered widespread governmental action along two lines: (l) An effort to identify those chemicals and conditions that give rise to malignant processes has been mounted by the Carcino genesis Testing Program, the National Cancer Program, and subse quently, the National...