The introduction of semi-automatic external defibrillators (SAEDs) allowed emergency medical technicians (EMTs) to deliver electroshocks in cases of out-of-hospital ventricular fibrillation (VF) or ventricular tachycardia (VT), often many minutes before the arrival of the mobile intensive care unit (MICU) team. In this observational study we report on the results obtained by the EMTs from the fire departments of Gent, Aalter and Brugge. In Gent, an SAED project started in May 1991. By December 1995, the SAED's electrodes had been attached in 367 cardiac arrest patients. The first rhythm detected by the device was asystole or electromechanical dissociation (EMD) in 241 patients (66%): only 5 of these patients survived to hospital discharge (2%). In the remaining 126 VF/VT cases (34%) the survival rate was 21% (26/126). In 14 of these 26 patients the shock(s) delivered by the EMTs restored spontaneous circulation before the arrival of the MICU team, with only venous cannulation and/or intubation being performed by the MICU team. In 4 other VF patients, the shock(s) delivered by EMTs converted the VF, with the MICU team successfully taking care of VF/VT relapses or postcountershock EMD. In the remaining 8 VF/VT cases, only the MICU attempts could resuscitate the patient. The SAED project in Aalter was set up in April 1993. By December 1995, care was taken for only 21 patients. None of the 4 VF/VT patients and the 17 asystole/EMD patients survived. In Brugge, there were 240 cardiac arrest cases treated with SAED between January 1991 and December 1995. Among the 89 VF/VT cases, there were 20 survivors (22%): 8 cases survived thanks to SAED shock(s) delivered by EMTs, in 3 cases survival was due to the combination of SAED shock(s) by EMTs and extensive ALS treatment by the MICU team, and in 9 cases restoration of spontaneous circulation was only obtained after application of ALS techniques by the MICU team. This observational study seems to show a beneficial effect of the introduction of SAED in Gent and Brugge. In Aalter the number of treated cases is tool low to draw conclusions. Anyhow, the global survival rate in the three areas remains low. Therefore, more efforts are needed to strengthen the other links of the chain of survival (early access to the emergency medical services-system, early basic cardiopulmonary resuscitation and early advanced life support.