During a one-year period, six patients were admitted to the hospital in diabetic ketoacidosis following 12 to 24 hours of illness at home. Urine testing with strips impregnated with sodium nitroprusside had indicated that no ketone bodies were present. Nine of 11 bottles of reagent strips in use for less than three months by these and other patients contained totally unreactive strips. Nitroprusside tablets exposed more than three months continued to give accurate readings.