This study is concerned with the value of basic CPR (manual ventilation and closed chest cardiac massage) initiated within 5 min in delaying brain damage after cardiac arrest in adult patients at ambient temperature. In 88 cases of cardiac arrest, basic CPR was initiated within 5 min of collapse by trained ambulance personnel. Basic CPR was continued during transport to the hospital in ambulances not equipped with defibrillators. Advanced CPR was instituted in all patients upon hospital arrival. All 11 patients eventually discharged from the hospital without apparent brain damage arrived at the hospital within 10 min of cardiac arrest. A significant number of patients arriving later could be resuscitated acutely but later died unconscious or were discharged with severe brain damage. We conclude that basic CPR, including bystander CPR initiated within 5 min of cardiac arrest is likely to be of long-term value only if definitive advanced life support can be provided within 10 min after the patient's collapse.