A number of electronic apex locators are available for use during endodontic treatment. The use of third and fourth generation electronic apex locators (EAL) are recommended to help clinicians determine the apical limit of the root canal system (RCS). The presence of different irrigating media in the RCS does not impact significantly on the performance of third/fourth generation apex locators. The devices are most accurate at determining the apical limit when the attached endodontic file contacts the periodontal ligament space and the visual analogue displays 'Apex' or '0.' Given the accuracies of modern generation EALs, the clinician should be able to consistently identify the apical limit of the tooth under treatment. Their use in conjunction with appropriate radiographs and the clinician's knowledge of average RCS lengths and anatomy will maximise the successful outcome of any orthograde endodontic treatment.