I suspect that many readers are unfamiliar with the concept of, evidence for, or implications of, the biological principle of hormesis.¹ This is a shame, insofar as environmental policy purports to be based on scientific evidence.² There is a substantial body of evidence behind the theory that even very hazardous substances have a hormetic pattern of effects—that is, they may be beneficial to health at very low levels of exposure.

The evidence for hormesis has received virtually no attention in environmental regulation, perhaps because the concept is seen as a "front" for industry efforts at deregulation.³ Yet one sincerely concerned with public health, and not merely concerned with opposing industry, must take hormesis seriously. This Dialogue seeks to do so. I explore the implications of hormesis in the context of environmental regulation of carcinogens, where it represents the greatest departure from prevailing regulatory theory.