Electroanalysis offers tremendous promise for scaling down analytical systems, with features that include high sensitivity, inherent miniaturization, low cost, low-power requirements, and high compatibility with advanced micromachining and microfabrication technologies. This article reviews the development of portable electrochemical analyzers for near-patient clinical testing, for on-site environmental monitoring, and for decentralized genetic testing. There is discussion of the challenges of creating a true 'Lab-on-a-Chip' and of integrating multiple electrochemical techniques and sensing schemes into a compact hand-held meter. Such microscale electrochemical systems hold great promise for meeting the needs and challenges of analytical chemistry in the twenty-first century. (C) 2002 Published by Elsevier Science B.V. All rights reserved.