Here we will discuss the development of arrays of mammalian cells of differing phenotype integrated with microfluidics and microsensors for applications such as drug screening and used to monitor cellular effects of multiple chemical and biological candidates. To fabricate these arrays, we immobilized either single or small groups of cells in 3-dimensional poly(ethylene glycol) hydrogel microstructures fabricated on plastic or glass surfaces. These microstructures were created using either photolithography or printed using microarray robots. The resulting hydrogel microstructures were fabricated to dimensions as small as 10 microns in diameter with aspect ratios as high as 1.4. The gels were highly swollen with water to permit mass transfer of nutrients and potential analytes to the cells, and cell adhesion molecules were immobilized in the gel to allow cell attachment and spreading. Cell viability was confirmed using fluorescent assays and ESEM used to verify complete cell encapsulation. The specific and non-specific response of these cells to target molecules was monitored using optical or electrochemical detectors and analyzed to quantify the effect of these agents on the different phenotypes present in the array.