Major urinary protein 1 (Mup1), also known as Mup7, Up-1, Ltn-1, Mup-1, Mup-a, Mup10 and Lvtn-1, is a low molecular weight secreted protein produced predominantly from the liver. Structurally it belongs to the lipocalin family, which carries small hydrophobic ligands such as pheromones. It has been demonstrated that Mup1 is an important player in regulating energy expenditure and metabolism in mice. In both dietary and genetic obese mice, the circulating concentrations of Mup1 were markedly decreased compared with the lean controls. Replenishment of recombinant MUP-1 led to improved glucose tolerance and insulin sensitivity, as well as increased energy expenditure and locomotor activity in db/db diabetic mice. It was suggested that Mup1 also regulates systemic glucose and/or lipid metabolism through the paracrine/autocrine regulation of the hepatic gluconeogenic and/or lipogenic programs, respectively.