In biology, Input and output (I&O) is the measure of food and fluids that enter and exit the body. Certain patients with the need are placed on I & O, and if so, their urinary output is measured. With self-toileting patients on I & O, or those who are assisted to a regular toilet or portable commode, a receptacle is placed in the toilet bowl that catches all urine that is put out by the patient. This, in turn, is measured by the nursing staff and recorded prior to its disposal.