5' nucleotidase activity in the human synovial lining in rheumatoid arthritis

5'-Nucleotidase (EC 3.1.3.5), a plasma membrane-bound enzyme, has been assayed in unfixed tissue sections of human synovium, activity being measured by scanning and integrating microdensitometry. Activity was markedly increased in the lining cells of the rheumatoid synovial membranes.