A review. Bilirubin was long considered a useless metabolite of heme catabolism, responsible for the clinical manifestation of jaundice, and potentially toxic in high doses, particularly in neonates. In the past two decades the potent biological properties of bilirubin, particularly as an antioxidant, have been recognized, and this has prompted a number of investigations into this molecule concerning its in vitro and in vivo properties. This review summarizes that work, as well as more recent investigations into the potential therapeutic uses of bilirubin.