Cardiopulmonary resuscitation (CPR) initiated by a bystander prior to arrival of the ambulance increases the chance of survival 2-3 times. Unfortunately a majority of patients do not receive such treatment. One way to approach the problem is to let the dispatcher instruct the witness in CPR via telephone when a presumed cardiac arrest occurs. In a recently performed study in Seattle patients with a presumed cardiac arrest were randomized to receive either traditional CPR (mouth-to-mouth ventilation plus chest compressions) or only chest compressions. Treatment was given by a witness via telephone instruction by the dispatcher. Among patients who only received chest compressions 14.6% could be discharged from hospital compared with 10.4% among patients who received traditional CPR. The difference was not significant. The results indicate that telephone instruction in CPR when a presumed cardiac arrest occurs might in certain cases preferably be restricted to chest compressions. The results of the trial are, however, difficult to translate into Swedish conditions, since ambulance response times in Sweden are much longer than in Seattle.