In 1924, she received the University of Chicago's Howard Taylor Ricketts Prize for work she began at Yale and continued in Chicago. At Yale she reported a curious finding: intravenous injections often caused fever in patients. Seibert determined that the fevers were caused by toxins produced by the bacteria. The toxins were able to contaminate the distilled water when spray from the boiling water in the distillation flask reached the receiving flask. Seibert invented a new spray-catching trap to prevent contamination during the distillation process. She published her pyrogen-free process in the "American Journal of Physiology". It was subsequently adopted by the Food and Drug Administration, the National Institutes of Health, and various pharmaceutical firms. She was further recognized in 1962 with the John Elliot Memorial Award from the American Association of Blood Banks for her work on pyrogens.