Therapeutic hypothermia (TH) improves the outcomes of cardiac arrest (CA) survivors. The aim of this study was to evaluate retrospectively the efficacy and safety of an immediate prehospital cooling procedure implemented just after the return of spontaneous circulation with a prehospital setting. During 30 months, the case records of comatose survivors of out-of-hospital CA presumably due to a cardiac disease were studied. A routine protocol of immediate postresuscitation cooling had been tested by an emergency team, which consisted of an infusion of large-volume, ice-cold intravenous saline. We decided to assess the efficacy and tolerance of this procedure. A total of 99 patients were studied; 22 were treated with prehospital TH, and 77 consecutive patients treated with prehospital standard resuscitation served as controls. For all patients, TH was maintained for 12 to 24 hours. The demographic, clinical, and biological characteristics of the patients were similar in the 2 groups. The rate of patients with a body temperature of less than 35 degrees C upon admission was 41% in the cooling group and 18% in the control group. Rapid infusion of fluid was not associated with pulmonary edema. After 1 year of follow-up, 6 (27%) of 22 patients in the cooling group and 30 (39%) of 77 patients in the control group had a good outcome. Our preliminary observation suggests that in comatose survivors of CA, prehospital TH with infusion of large-volume, ice-cold intravenous saline is feasible and can be used safely by mobile emergency and intensive care units.