The authors experienced a case of plasma cholinesterase variant who received succinylcholine, atracurium and reversal with pyridostigmine, and showed prolonged neuromuscular blockade postoperatively, and was ventilated artificia1ly until complete recovery. The patient and her two children later gave samples of blood. The patients blood revealed very low plasma cholinesterase activity of 0.11 IU/L(normal range; 5-12 IU/L) and dibucaine number of 33. In consideration of her childrens plasma cholinesterase activities and dibucaine numbers, we suggest that she has genetically abnormal plasma cholinesterase and probably her genotype is E E or E E.