 In a previous study pre-treatment with intravenous MgSO4 60 mg kg-1 was not shown to have any impact on the onset of action of rocuronium Kussmann et al, 1997. Yet, in that study, MgSO4 was injected as a bolus after induction of anaesthesia, one minute only before the injection of the neuromuscular blocking agent. We suppose that magnesium needs some time to penetrate the neuromuscular endplate and to shift the MgCa ratio in favor of magnesium. Thus, the particular design of the previous study may explain why magnesium had no scope to enhance the speed of onset of action of rocuronium. 