This is the twelfth in a series of conferences on environmental toxicity sponsored by the Department of Radiation Biology and Bio physics. The topics selected are intended to be of timely interest with a focus somewhat different from those with with similar titles. I would like to share with you some of the thought which went into the development of this year's program. Everyone here is aware of the great amount of publicity being given to some phase of this year's topic of "Polluted Rain," but I wonder how many of the younger generation realize how the entire world got into this kind of...