Implementation of the goals of each EPA regulatory program requires the use of laboratory test data to determine the toxicological properties of the chemical substances being regulated. This information is then used to predict the potential impact of a material on the environment. Since the implementation of the 'Acts', considerable research effort has been devoted to developing a wide variety of biological toxicity tests to define the effects of chemicals on organisms and communities. The purpose of this paper is to examine how various types of toxicological data are organized, interpreted and utilized in making regulatory decisions. Two Approaches are examined in detail. First, the strategy used for developing water quality criteria for the protection of aquatic life. Second, the concept of hazard assessment is examined emphasizing both the similarities and differences with the criteria strategy. Finally, a retrospective case study is presented for each strategy to illustrate the relationship between the predictions derived from laboratory toxicity tests and field observations.