In March 1984, the U.S. Environmental Protection Agency (EPA) issued a significant change in procedures regulating toxic materials in effluents through the National Pollutant Discharge Elimination System (NPDES). Concurrent with this toxicity-based effluent control policy, the EPA established the marine/estuarine component of the Complex Effluent Toxicity Testing Program (CETTP). The CETTP was established to provide reliable, sensitive and environmentally meaningful test protocols that could be used to detect toxic industrial and municipal effluents within the NPDES. Five toxicity test methods have been developed and validated for the program since 1984 using a marine plant (Champia parvula), two invertebrate species (Arbacia punctulata and Mysidopsis bahia) and two fish species (Cyprinodon variegatus and Menidia beryllina). The laboratory precision test results for the methods were acceptable; coefficients of variation for all methods were less than 54%, averaging 34%. Numerous field tests were conducted using these methods and the results indicate that tests on receiving waters (in which effluent concentrations could be estimated through controlled dye studies) accurately reflect the toxicity of the effluents measured directly. Receiving water impacts, when observed, were generally near-field in nature.