Pseudocholinesterase is an essential enzyme for hydrolysis of succinylcholine and some people has low activity. The pseudocholinesterase from a normal individual has a greater apparent affinity for the cholinester substrate than the enzyme from succinylcholine-sensitive individuals, who has genetic variants. The ideal situation would be one in which a single, simple test would detect and identify all the variant forms of enzyme, but no such test currently exsits. The inhibitors frequently used to identify variants are dibucaine, fluoride, chloride, urea or succinylcholine as inhibition numbers. The authors found that dibucaine, fluoride and chloride numbers in Korean adults (mean±SD, %) are 85.8±1.83, 46.5±2,05 and 3.53±1.64, respectively (substrate is butyrylthiocholine).