More than 1 5 0 0 different halogenated chemicals are produced and discharged into our biosphere by plants, marine organisms, insects, bacteria, fungi, and other natural processes. In a few cases, the quantities of these naturally occurring halogenated compounds far exceed the amounts of the same chemicals from anthropogenic sources. Furthermore, the evidence is overwhelming that natural enzymatic, thermal, and other processes are constantly occurring in the oceans, in the atmosphere, and in the soil that lead to the formation of chlorinated and brominated phenols and many other halogenated chemicals, including dioxins, that previously were thought only to result from the actions of man. Moreover, it is clear that these natural processes have been producing halogenated compounds and have been an important component of our ecosystem for eons.