Purple urine drainage bags were found in 7 of 71 chronically catheterized elderly women. The purple staining of the bags is due to a violet discoloration (indirubin) of the plastic of the catheter bag and fine blue crystals of indigo in the urine. The colors are formed from the substrate indoxyl sulfate (indican) and all 7 patients had bacteria in the urine that would produce blue colonies on agar enriched with the urine (filter sterilized) of the patients involved. Organisms identified were Providencia or Klebsiella species. Indican excretion was higher in patients with purple urinary catheter bags than in controls.