The search for new muscle relaxants is an attempt to improve on the undesirable pharmacologic properties of currently available nondepolarizing muscle relaxants. Ideally, new muscle relaxants would exhibit fewer cardiovascular hemodynamic side effects, have fewer cumulative effects, possess rapid onset of and shorter durations of action, and be less dependent on hepatic and/or renal function for metabolism and excretion. Furthermore, drug metabolites should be pharmacologically inactive. Two new nondepolarizing muscle relaxants, vecuronium (Norcuron) and atracurium (BW 33A), are examples of drugs approaching these ideal muscle-relaxant characteristics. Currently, these drugs are used clinically in Europe and are undergoing clinical trials in this country.