This workshop is the third of a series of workshops sponsored by the Round- table on Environmental Health Sciences, Research, and Medicine since the Roundtable began meeting in 1998. When choosing workshops and activities, the Roundtable looks for areas of mutual concerns and also areas that need further research to develop a strong environmental science background. The Roundtable delegated the planning of this workshop to a planning group. The group was headed by Donald R. Mattison and Samuel Wilson, who were in- volved in the editing of this summary