A combination of forces is converging to promote the development of biosensors that are capable of measuring multiple analytes simultaneously. First is customer demand; no longer are most users satisfied with analyzing each sample for one target at a time. Second, the development of microarrays for genomic applications has demonstrated the potential to measure hundreds or even thousands of targets simultaneously in laboratory systems. Third, biosensor technology itself has become more familiar both to scientists and to users as an inexpensive alternative to centralized laboratories and offers both fast response and on-site analysis. An ideal biosensor that detects multiple analytes would also be portable and fully automated to facilitate on-site use by a variety of users. Array biosensors offer the most promising approach to achieving this goal.