Summary Summary: Muscle relaxants are used in modern anaesthesia for almost 60 years. This review covers the physiology of neuromuscular transmission, the mechanism of action, the sensitivity of different muscles, and the pharmacologic priniciples of neuromuscular blocking agents. According to the duration of action, the pharmacologic profiles of the currently available muscle relaxants are described. Today safety and economic issues influence the choice of muscle relaxants. The duration of action and side effect profile allows to select the most appropriate muscle relaxant. For pharmacoeconomic evaluation of neuromuscular blocking agents not only acquisition costs have to be considered but the total cost of hospital stay and treatment. The modern muscle relaxants have less side effects, accelerate operating room turn over, shorten hospital stay and improve outcome. Although their acquisition costs are higher they are cost effective.