Physiologic monitoring systems monitor vital physiologic parameters so that clinicians can be informed of changes in a patient's condition. They typically consist of several distinct components, including a central station, bedside monitors, and ambulatory telemetry transmitters and receivers. We previously evaluated physiologic monitoring systems in our January-February 1999 issue (Health Devices 28[1-2]). For this update, we have tested systems from two additional suppliers, using the same criteria and test methods that we used for the eight systems in the original study. As in the earlier Evaluation, we have examined how each system functions as a whole, rather than focusing on the performance of individual components. We judged the systems primarily on adaptability, alarm implementation, and human factors design. In the Conclusions, we compare all 10 units evaluated to date. We also provide updated product information for the systems evaluated in our original study; in some cases, the changes that have been made to those systems have caused us to revise our ratings. We rated all the systems based on their capabilities for each of six applications: (1) critical care unit, (2) emergency department, (3) intermediate care unit and general medical/surgical floor, (4) operating room, (5) postanesthesia care unit, and (6) transport. As in our earlier study, we have determined that most of the evaluated systems have drawbacks for one or more of the evaluated applications. In our January-February 1999 Evaluation of physiologic monitoring systems (Health Devices 28[1-2]), we discussed the issues surrounding the purchase and use of these systems. In this introduction, we recap the most significant points from that discussion, provide some new information about ambulatory telemetry and wireless networks, and briefly describe the components of this Update Evaluation.