Remifentanil has important side effects and it is not easy to know what remifentanil concentrations should be used during different endpoints of anaesthesia. We analyzed the remifentanil predicted effect-site concentrations (RemiCe) at different events during neurosurgical procedures and assessed if the concentrations used were clinically adequate. BIS and haemodynamic parameters were collected every 5 seconds. Predicted cerebral concentration of propofol (PropCe) and RemiCe were analyzed immediately prior to respective stimulus, and 30, 60 and 90 seconds after. RemiCe were 2.2 +/- 0.3, 6 +/- 2.6 and 2.2 +/- 0.9 ng ml(-1) at intubation, incision and extubation, respectively. PropCe observed in the same periods were 5 +/- 1, 2.6 +/- 0.9 and 1 +/- 0.3 microg ml(-1), also respectively. The remifentanil concentrations used in our patients were lower than reported concentrations, while being clinically adequate to minimize the haemodynamic response to stimulation.