1. Highly sensitive techniques are described for the assay of plasma membrane (5′-nucleotidase, alkaline phosphatase), microsomal (neutral α-glucosidase, leucyl-2-naphthylamidase) and biliary canalicular (γ-glutamyltransferase) enzymes and for nine acid hydrolases (acid phosphatase, phosphodiesterase, β-glucosidase, α-glucosidase, α-galactosidase, β-galactosidase, α-mannosidase, N-acetyl-β-glucosaminidase, β-glucuronidase) in human liver.
2. Optimum and specific assay systems have been developed which give linear kinetics for all enzymes.
3. The range of enzyme activities in samples of human liver, obtained by closed needle biopsy, and in sera have been determined.