Currently, only single-lead, serial telemetry rhythm strips can be transmitted from ambulances. Triage of patients with chest pain and administration of thrombolytic therapy in ambulances is limited by the lack of specific electrocardiographic (ECG) diagnosis. A new technique is described using cellular telephone transmission of simultaneous 12-lead ECGs from ambulance to hospital to overcome this limitation. A portable 12-lead ECG installed in an ambulance was connected via modern link to a cellular telephone and digitized ECG information was transmitted to an ECG device in the hospital emergency room. Paramedics in the field placed adhesive patch electrodes and attached ECG wires. Field ECGs from 23 patients were compared with corresponding transmitted ECGs. There were no differences in heart rate, PR interval, QRS duration, QT interval or R- and T-wave axes. Baseline and transmitted ECGs had identical morphologic characteristics. Differences in R-wave amplitude in 5 transmitted tracings compared with hospital-recorded ECGs resulted in computer diagnosis of left ventricular hypertrophy by voltage, possibly due to differences in patient position. Twelve-lead ECGs can be easily transmitted from a moving ambulance using cellular telephones. This allows diagnosis before hospital arrival, improves prehospital triage of patients and may facilitate prehospital therapy with lidocaine or streptokinase. In addition, the cellular telephone link can convey both verbal and digitized information and thus improve on current telemetry systems.