The use of an artificial kidney in dogs frequently resulted in reactions consisting of vomiting, shivering, diarrhea, and a prolonged fall in blood pressure. These reactions appeared to be due to the contact of the dog's blood with the cellophane. Aqueous extracts of cellophane were prepared which produced similar reactions when injected intravenously into dogs. These hypotensive substances could be removed from the cellophane by extraction with boiling water for twelve to fifteen hours. The use of such treated cellophane in the artificial kidney almost completely eliminated undesirable reactions in the dog during dialysis.