Neuromuscular blocking (NMB) drugs, or “muscle relaxants” produce paralysis of the skeletal muscles. They may be used either to aid stable mechanical ventilation by blocking spontaneous respiratory movements or, more frequently, to provide more suitable conditions for surgery. If skeletal muscle tone is eliminated by using a NMB agent, exposure of the surgical site can be achieved more easily and with less trauma to the surrounding tissues. NMB drugs are also used in neurophysiological and other studies, to enable very light planes of anaesthesia to be maintained. Under these conditions, if an NMB had not been administered, spontaneous muscle movements could occur which would interfere with data collection.