Potential risks to the environment have become considerably more prominent in the investigation of hazardous waste sites. The paradigm for conducting risk assessment, as articulated by the National Research Council, is geared primarily towards the assessment of potentially adverse health in humans. Subsequent detailed guidance published by the Environmental Protection Agency has also focused on the protection of the human health. In spite of the scientific complexity, potentially high costs of conducting ecological risk assessments, and lack of regulatory guidance, a relatively straightforward method for assessing ecological risks at hazardous waste sites has been developed. The method comprises a series of phases including a preliminary phase to gather information and formulate problems and three active phases. The active phases include (1) risk screening to estimate risk to keystone ecological receptors through an ecological toxicity quotient method; (2) initial investigations that may include field or laboratory work to assess the health of the community of exposed receptors through activities that may entail collection and analysis of tissue samples, bioassays, bioavailability studies or, if needed, a biodiversity study; and (3) detailed investigations that determine the potential adverse effects of contamination over several life cycles of the species of concern through population studies or studies of the life history-habitat requirements of given species. The method is designed to encourage evaluation of the results at the end of each phase so that remedial decisions can be made as expeditiously as possible. The entire three phases need not be completed in many cases.