AbstractA micromethod of serum cholinesterase activity determination is presented. The changes in activity levels in uremic patients requiring hemodialysis are presented in relation to blood transfusions, blood urea nitrogen, and serum creatinine levels, as well as hematocrit percentages. The levels were low in uremic patients and were further affected by hemodialysis. The values of serum cholinesterase in patients with renal allografts as well as the renal vein effluent of isolated perfused canine kidneys have been determined. These levels were near a normal range. It is suggested that anesthesia in uremic patients necessitating muscle relaxation with an agent that hydrolyzes cholinesterase should be deferred for 24 hr after hemodialysis.