The "biliary tract" enzymes (leucine aminopeptidase, gamma-glutamyltranspeptidase and 5'-nucleotidase) in serum reflect to varying degrees, obstruction, proliferation, inflammation and neoplasia involving the hepatobiliary duct system. Their use is directed towards two purposes: (1) as non-electrophoretic assays to evaluate the source of an elevated non-specific alkaline phosphatase and (2) to offer greater sensitivity and specificity for space-occuping lesions in the liver. In appropriate

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... cal states, any of the three enzymes offer these advantages and there is little to chose among them. Selection of the assay to use in the clinical laboratory then becomes based on non-clinical factors, i.e., technical ease, apparent substrate specifities, etc. With these additional factors and despite some shortcomings, our selection is leucine aminopeptidase.