Alpha-1-microglobulin (α1-MG) is a microglobulin, a small globular protein. It is found in all vertebrates, including humans, and is distributed in blood plasma and extravascular tissues of all organs. It is synthesized in most cells of the body, but mainly in the liver from a gene that codes for the alpha-1-microglobulin/bikunin precursor.

α1-MG binds and degrades heme, is a radical scavenger as well as a reductase. A model has been proposed in which α1-MG is described as a circulating “waste bin” which continuously removes free radicals and oxidizing agents, particularly heme, from the tissues. It is subsequently transported to the kidneys, where it is broken down. The protein is therefore believed to protect cells and tissues against the damage that is induced by abnormally high concentrations of free hemoglobin and/or reactive oxygen species.