To establish itself as a legitimate discipline, aquatic toxicology must not become static—content with resolving old problems—but must always be willing to move into new and different areas. There are a number of research needs in aquatic toxicology which deserve the attention of investigators. We need research programs in aquatic toxicology which ask the question of how chemicals affect aquatic organisms. Generally, in the past we have only been concerned if a chemical kills an organism or if it prevents reproduction, but not with how it does these things. More research is needed to illucidate the chemical mechanisms and modes of action. Perhaps from this we can develop better chemical structure-activity relationships. Basic research into anatomy, physiology, nutritional requirements, pathology, and life histories of our test organisms is needed. We need a major research program to determine if the chronic effects we observe in our laboratories, such as depressed reproduction and growth, have ecological significances. Through better knowledge of life histories and the use of population modeling, perhaps it will be possible to meet this need. It is essential that we develop test methods and a data base which identify how chemicals affect an ecosystem's functional processes. Ecologists recognize the value of protecting ecosystem functions but have only primitive tools with which to assess the potential impacts of chemicals on these functional processes. Studies must be conducted to identify when a chemical is biologically available. Are sorbed materials biologically available? Finally, researchers in aquatic toxicology should explore the efficacy of aquatic test organisms as surrogates for humans. Screening chemicals for potential health effects by using fish or other aquatic organisms has many advantages over currently used mammalian toxicology test species, low cost being a prime example. However, knowledge of the metabolism and physiology of aquatic test species must be established.