The Tamm–Horsfall glycoprotein (THP), also known as uromodulin, is a glycoprotein that in humans is encoded by the UMOD gene. Uromodulin is the most abundant protein excreted in ordinary urine.

Uromodulin excretion in urine follows proteolytic cleavage of the ectodomain of its glycophosphatidylinositol-anchored counterpart that is situated on the luminal cell surface of the loop of Henle. Uromodulin may act as a constitutive inhibitor of calcium crystallization in renal fluids. The excretion of uromodulin in urine may provide defense against urinary tract infections caused by uropathogenic bacteria.

Uropontin, nephrocalcin and uromodulin (this protein) are the three known urinary glycoproteins that affect the formation of calcium-containing kidney stones or calculus. Tamm–Horsfall protein is part of the matrix in renal calculi but a role in kidney stone formation remains debatable. However, decreased levels of Tamm–Horsfall in urine have been found to be a good indicator of kidney stones. Defects in this gene are associated with the autosomal dominant renal disorders medullary cystic kidney disease-2 (MCKD2) and familial juvenile hyperuricemic nephropathy (FJHN).