As part of the US EPA’s research effort to evaluate the potential for toxic materials and genetically engineered microorganisms (GEMs) to cause environmental change, our research has focused on the development of ecological procedures to measure the response of soil foodweb organisms to anthropogenic stressors. Specific aims of this research have been to: (a) discern the response and determine the mechanisms underlying the response of foodweb components to the presence of stressors and (b) develop indicator techniques and assessment protocols to assess environmental changes that are observed. This work has shown that the microbial portion of the foodweb in soil culture responds to anthropogenic stressors in a predictable fashion as do higher life forms. If the stressor is toxic, susceptible populations will die. If the stressor can be metabolized and the metabolic product is toxic, a portion of the microbial population may utilize the material and grow, while other organisms may die. This susceptibility phenomenon is well known to public health professionals, but perhaps less to the environmental microbiologist. Key to our understanding and predictive management of this relationship is the development of new indicator techniques that are sensitive to environmental changes and can predict vulnerable microbial communities. Indicators must warn of consequences before the system of interest reaches a threshold of no return. Therefore, the problem we face is to design and conduct unambiguous research which shows when indicators are highly predictive of changes that are to come and, conversely, to clearly demonstrate when the indicators are inappropriate to warn of potential consequences.