The purpose of this study was to compare the incremental, cumulative dose method and the single bolus injection technique for construction of dose‐response curves for vecuronium. Dose‐response curves were determined in 77 patients divided into four groups according to the anaesthetic given and the method used for construction of dose‐response curves. The regression lines corresponding to the four dose‐response curves were found to be parallel. For vecuronium ED₅₀ during neurolept anaesthesia was found to be 28 μg kg^‐1 with the single bolus injection technique and 35.2 μg kg^‐1 with the incremental, cumulative dose method (P<0.05). During halothane anaesthesia, ED₅₀ was found to be 25.7 μg kg^‐1 and 26.2 μg kg^‐1, respectively (P>0.05). Potentiation of vecuronium by halothane was found with the cumulative method only. It is concluded that the incremental, cumulative dose method is not suitable for potency determinations of vecuronium.