||The U.S. Environmental Protection Agency (EPA) and the National Cancer Inst. (NCI) have major responsibilities for determining the fate and risks of carcinogenic agents in the natural environment. Under the auspices of EPA/NCI, the Carcinogen Research Team at the USEPA Lab, Gulf Breeze, has a major role in investigating the fate, effects, and risks of carcinogenic agents in the aquatic portion of the biosphere. In regard to this role, there is a need for practical, experimental exposure systems for the short term, and long term exposure of fishes and invertebrates in order to evaluate their responses to environmentally significant carcinogens. A pilot test of the system has been completed. This test utilized flowing filtered, estuarine water, controlled water temperature, controlled photo period, controlled nutrition of test species, oxygen concentration monitoring, and various life cycle stages of the test fish, the sheepshead minnow, Cyprinodon variegatus, and the suspect carcinogenic herbicide, trifluralin. Continuous exposures to 1 to 5 micrograms/1 trifluralin were conducted with zygote, thru embryogenesis to adult stages of the fish.