Bilirubin IXalpha is a member of the class of biladienes that is a linear tetrapyrrole with the dipyrrole units being of both exovinyl and endovinyl type. A product of heme degradation, it is produced in the reticuloendothelial system by the reduction of biliverdin and transported to the liver as a complex with serum albumin. It has a role as an antioxidant, a mouse metabolite and a human metabolite. It is a dicarboxylic acid and a member of biladienes. It contains a 24G7 epitope. Bilirubin is a tetrapyrrole and a breakdown product of heme catabolism, it is a prominent endogenous antioxidant cytoprotectant and a natural inhibitor of vascular smooth muscle cell proliferation, which has neuroprotective and anti- atherosclerosis-related diseases effects. It can act as an effective agent to reduce mortality and counteract hypotension elicited by endotoxin through mechanisms involving a decreased NOS2 induction secondary to inhibition of NAD(P)H oxidase.