TCEP (tris(2-carboxyethyl)phosphine) is a reducing agent frequently used in biochemical and molecular biology applications. TCEP is often used as a reducing agent to break disulfide bonds within and between proteins as a preparatory step for gel electrophoresis. It is soluble in water and available as a pH-neutral stabilized solution immobilized on an agarose support to facilitate the removal of the reducing agent.

Compared to the other two most commonly used reducing agents dithiothreitol (DTT) and β-mercaptoethanol (BME), TCEP has the advantages of being odorless, a more potent reducing agent, irreversible (in the sense that TCEP does not regenerate - the end product of disulfide cleavage by TCEP is actually two free thiols/cysteines), more hydrophilic and more resistant to oxidation in air.

TCEP is particularly useful for the labeling of cysteine residues with maleimides.