A bacterial species typically includes heterogeneous collections of genetically diverse isolates. How genetic diversity within bacterial populations influences the clinical outcome of infection remains mostly indeterminate. In part, this is due to a lack of technologies that can enable contemporaneous systemslevel interrogation of host-pathogen interaction using multiple, genetically diverse bacterial strains. This chapter presents a prototype microfluidic cell array (MCA) that allows simultaneous elucidation of molecular events during infection of human cells in a semi-automated fashion. It shows that infection of human cells with up to sixteen genetically diverse bacterial isolates can be studied simultaneously. The versatility of MCAs is enhanced by incorporation of a gradient generator that allows interrogation of host-pathogen interaction under four different concentrations of any given environmental variable at the same time. Availability of high throughput MCAs should foster studies that can determine how differences in bacterial gene pools and concentration-dependent environmental variables affect the outcome of host-pathogen interaction. © 2011, IGI Global.