PROLONGED paralysis and apnea following the administration of the muscle relaxant succinylcholine are an uncommon clinical Occurrence. The drug is normally hydrolyzed and inactivated by serum cholinesterase. An abnormality of the enzyme may result in persistence of the depolarization block of neuromuscular transmission induced by succinylcholine.1 Materials and Methods Human serum was submitted to vertical starch-gel electrophoresis2 at pH 8.75 according to a method described previously.3 The samples were inserted in the gel on strips of filter paper.4 In some experiments an increased quantity of serum was applied to the gel by placing at the origin four strips of filter paper saturated with serum instead of one. A voltage gradient of 12/cm was applied for three hours at 4 C. To demonstrate esterase activity the sliced gel was incubated for 16 hours at 4 C in a medium similar to that described by Hunter and