This study is an update to our August-September 1995 Evaluation of automated external defibrillators (AEDs) in which we evaluated nine AEDs from three manufacturers. In the current issue, we evaluate three additional semiautomated AEDs from three manufacturers. (We also present update information, including new rankings, for the previously evaluated units.) We tested the new units against the same criteria and rated and ranked them using the same scheme as in our original Evaluation. Specifically, we judged the suitability of these units for two primary clinical applications: prehospital use and in-hospital use. In addition, in this Update, we rated and ranked all of the units evaluated to date for a third clinical application: public access defibrillation (PAD) use. In this Update, we briefly describe the purpose and use of AEDs in the Introduction. For more detailed information about this technology, the environments in which AEDs are used, and the factors to consider when selecting this type of device, we encourage readers to refer to our original AED Evaluation (Health Devices 24[8-9], August-September 1995). Also, because our criteria and test methods have not changed since the original study, we have not repeated them in this issue. Again, readers should refer to the previous Evaluation for this information. Furthermore, as described in the inset on page 272, the format of this Update differs from that of traditional Health Devices Evaluations. Most notably, all of the characteristics, test results, and ratings for each unit are presented in an individual Product Profile. Following the profiles for the three units, we present a comprehensive Conclusions section, detailing how the newly evaluated units compare with those evaluated in our original study.