The central figure in developing the 1970 US Clean Air Act, Senator Edmund Muskie, rather plaintively asked that the scientific information underlying this act be obtained from a onehanded scientist. He was tired of hearing scientists saying "on the one hand. .. , yet on the other hand.. .. " The Senator was expressing the desire of lawmakers for indisputable scientific facts on which to base regulatory actions. Unfortunately, this is not the way science works, particularly in situations where there is uncertainty concerning the questions being asked, or the terms being used. Lack of clarity in definition or consistency in use is a particular problem when considering the Precautionary Principle. My discussion of the impact of the Precautionary Principle will inevitably fall into the "on the one hand. .. , yet on the other hand. .. " category that made Senator Muskie so unhappy. I will argue that the precautionary principle is both good public health and that it is causing public health problems; that it will both increase and decrease the importance of toxicological science in decision making; and that the European Community (EC) is both using the Precautionary Principle in some innovative ways to protect public health and the environment, and that the EC is intentionally abusing the precautionary principle by using it as a means to erect artificial trade barriers not warranted by toxicological science and risk analysis.