This study was designed to compare the effects of ketamine and alfentanil administered prior to induction of anaesthesia with propofol, on the haemodynamic changes and ProSeal laryngeal mask airway((R)) (PLMA) insertion conditions in children. Eighty children, aged between 3-132 months, were randomly allocated to receive either alfentanil 20 mu g.kg(-1) (alfentanil group) or ketamine 0.5 mg.kg(-1) (ketamine group) before induction of anaesthesia. Ninety seconds following the administration of propofol 4 mg.kg(-1), a PLMA was inserted. In the ketamine group, heart rate and mean arterial pressure were higher during the study period compared with the alfentanil group (p < 0.05). The time for the return of spontaneous ventilation was prolonged in the alfentanil group (p = 0.004). In conclusion, we found that the administration of ketamine 0.5 mg.kg(-1) with propofol 4 mg.kg(-1) preserved haemodynamic stability, and reduced the time to the return of spontaneous ventilation, compared with alfentanil 20 mu g.kg(-1) during PLMA placement. In addition, the conditions for insertion of the PLMA with ketamine were similar to those found with alfentanil.