The actions of the new depolarization-blocking muscle relaxant agent; 2 beta,16-beta-bis-(4'-dimethyl-1'-piperazino)-3 alpha,17 beta-diacetoxy-5 alpha-androstane dibromide (pipecurium bromide, RGH-1106, Arduan), were studied in fentanyl-N2O, in halothane-N2O and in methoxy-flurane-N2O anaesthesia in a total of 94 patients. The drug in a dose of 0.05 mg/kg body weight (recommended by the manufacturer), elicited complete muscle relaxation, which was satisfactory even for performing abdominal operations. The effect occurred within 3-4 min, and subsided after 40-50 min. The residual effect had to be antagonized in 82% of the cases, and neostigmine had a satisfactory antagonizing effect in all patients. Transient fall of blood pressure and bradycardia (in 40.4% of the cases) were observed as side effects. Further studies are needed for the determination of the pathomechanism of bradycardia and to judge to what extent the inhalation anaesthetic agents influence the duration of action of pipecurium bromide.