ERYTHROCYTE acetylcholinesterase (AChE) is strongly bound to the cell membrane1. To isolate and purify this enzyme, it must be removed from the membrane and brought into solution. Methods used for this purpose have included treatment with butanol2, digestion with pancreatin3, or addition of a surface-active material4,5. More recently, we have succeeded in solubilizing the enzyme from bovine erythrocytes by disintegrating the lysed cells by ultrasonic vibration.