The use of behavioral endpoints in environmental hazard and impact assessment has become a major field of study in recent years. Although behavior has always been accepted as an important aspect of animal survival and ecology, toxicological research over the past two decades has concentrated primarily on lethality, growth, and reproductive success. In this review we discuss a broad range of chemical contaminants by comparing concentrations causing preference and/or avoidance with concentrations acute and chronic toxicity. Although previous reviews have been presented on various aspects of behavioral responses of fishes and invertebrates to aquatic contaminants (Anderson 1971, Sutterlin 1974, Schere 1977, Maciorowski et al, 1977, Larrik et al. 1978, Cherry and Cairns 1982, Cairns and van der Schalie 1981), no review to date has been found which systematically evaluates the relative sensitivities of the diverse testing methods.