The aim of the study is to compare anaesthesia (for back surgery) using endotracheal intubation (patients anaesthized in the supine position)with anaesthesia using a laryngeal mask (anaesthesia induced and the laryngeal mask placed with the patient in the prone position on the operation table) as regards advantages, adverse effects and time spent. The anaesthesia in the 2 groups of patients is identical (propofol, remifentanil, rocuronium). Two groups of 70 pt. each are included in the stud. The inclusion criterias are patients 18-70 yrs., ASA group 1-2, normal airways, patients scheduled for back surgery with an estimated duration of less than 2 hours.