The use of DNA and protein microarrays has revolutionized our understanding of living systems. This paradigm can be extended to the use of cell-based assays that can investigate the state of the cell at the level of an integrated system. Use of cellular microarray formats will allow the next generation of cell-based assays to be ultrahigh throughput. Techniques for micropatterning cells using surface chemical modification have been previously reported but suffer from lengthy patterning times (~ h). We have developed active arraying techniques to rapidly localize live cells on a 2-dimensional patterned electrode using electrophoresis (Figure 1). Previous studies have shown that the cells remain viable after exposure to an applied potential of 10 V or less. In this 2-dimensional system, cells may migrate and destroy the microarray format. Furthermore, some primary cells such as hepatocytes and chondrocytes lose phenotypic stability on 2-dimensional surfaces. Use of a 3-dimensional microarray platform may address these limitations.