1. A brown degradation product of hemoglobin, present in the feces.
2. A coloring matter found in the feces, a product of the alteration of the bile pigments in the intestinal canal; identical to hydrobilirubin (body formed from bilirubin*, identical with urobilin*).

*Bilirubin is a pigment produced when the liver processes waste products. A high bilirubin level causes yellowing of the skin.

*Urobilin is also a yellow pigment identical with hydrobilirubin, abundant in the highly colored urine of fever, and also present in normal urine.

Urobilin is a constituent of the brown pigment found in feces; which is derived from bilirubin by reduction due to bacteria in the intestine.