Ecotoxicology is the science that seeks to predict the impacts of chemi- cals upon ecosystems. This involves describing and predicting ecological changes ensuing from a variety of human activities that involve release of xenobiotic and other chemicals to the environment. A fundamental principle of ecotoxicology is embodied in the notion of change. Ecosystems themselves are constantly changing due to natural processes and it is a challenge to distinguish the effects of anthropogenic activities against this background of fluctuations in the natural world. With the frustratingly large diverse and ever-emerging sphere of envi- ronmental problems that ecotoxicology must address the approaches to individual problems also must vary. In part as a consequence there is no established protocol for application of the science to environmental prob- lem-solving. The conceptual and methodological bases for ecotoxicology are how- ever in their infancy and thus still growing with new experiences. In- deed the only robust generalization for research on different ecosystems and different chemical stresses seems to be a recognition of the necessity of an ecosystem perspective as focus for assessment. This ecosystem basis for ecotoxicology was the major theme of a previous pUblication by the Ecosystems Research Center at Cornell University a special issue of Environmental Management (Levin et al. 1984). With that effort we also recognized an additional necessity: there should be a continued develop- ment of methods and expanded recognition of issues for ecotoxicology and for the associated endeavor of environmental management.