An investigation of effects of pollutants on fish flavor was conducted on the Missouri River from Sioux City, Iowa, downstream to Waverly, Missouri. Test channel catfish were placed upstream and downstream from all known significant waste discharges in this reach. After four days exposure, they were removed, dressed, quick frozen, and submitted to a food-flavor test panel. Fish held in the Missouri River in a one mile reach downstream from slaughterhouses and industrial waste discharges at Sioux City, Iowa, had an unacceptable flavor. Downstream from the Council Bluffs and Twin Cities sewage discharges, caged fish acquired an unacceptable flavor. Downstream from the Omaha sewage treatment plant discharge, fish acquired the most unacceptable flavor of any tested in the study. Wastes from the Omaha sewage treatment plant caused an unacceptable flavor in fish for 2.5 miles of river along the Nebraska shore.