Bilirubin is an abundant, reddish-yellow bile pigment found in mammalian tissues and serum. The pigment has long been regarded as simply a cytotoxic waste product that needs to be excreted, as bilirubin in high concentrations can cause neurological damage. In recent years, however, increasing evidence suggests that bilirubin may also have functional importance. In vitro studies have demonstrated that bilirubin is an antioxidant substance. Other studies indicate that bilirubin may be capable of modifying or regulating immune functions. At present, however, the potential biological activities and physiological role of bilirubin is not well understood. Yingru Liu is studying the antioxidant effect of bilirubin, and exploring other physiological functions that bilirubin may also possess. Specifically, he is using an animal model to investigate the potential protective role of bilirubin as it relates to multiple sclerosis, a disease in which oxidative stress by free radicals and immunological factors play important disease-causing roles. His work may characterize the bile pigment system as an attractive target for drug therapy in multiple sclerosis. In addition, his research may have an impact on guidelines for treatment of an excess of bilirubin (such as neonatal jaundice and physiological hyperbilirubinemia). It may also confirm the need and potential methods of treating abnormally low levels of bilirubin.