Variations of plasma cholinesterase activity were studied in eight patients with end stage liver disease having orthotopic liver transplantation and five other patients with hepatic cirrhosis undergoing surgical procedures. Serum cholinesterase activity was found to be below normal limits in every patient, even more so in those having hepatic homotransplantation, probably because of the greater severity of their disease. Blood transfusions increased pseudocholinesterase activity to normal or nearly normal levels; but only after successful transplantation did these levels remain within normality, thus suggesting that the homografts promptly assume production of the serum enzyme.