Bovine liver alkaline phosphatase has been purified to homogeneity by procedures that include reverse-phase HPLC. The pure enzyme has an apparent M r of 160,000 and is composed of what appears to be two identical monomers of M r 82,000. About 80% of the material yielded the amino-terminal sequence Leu-ValProGluLysGlu LysAspPro?Tyr?ArgAspGlnAlaGln. The minor component was extended at the amino terminus by two residues that have not yet been identified, i.e., ?? LeuValProGluLysGluLysAspPro?Tyr?Arg AspGlnAlaGln.