Some in vitro physiological studies of liver -- such as drug metabolism and toxicity, cancer cell metastasis, regeneration, and response to chronic infection -- might best be carried out in a 3D culture system that mimics features of liver parenchymal architecture, including the very localized flow of fluid through tissue. We designed and implemented a perfusion microreactor that allows us to recreate many features of three dimensional liver tissue at the level of the smallest functional tissue unit, the capillary bed. Further, the design of the reactor allows us to probe tissue structure and function in a noninvasive manner via microscopy and can be scaled to hold 10,000 – 1,000,000 cells. Using a prototype system that allows in situ imaging, we showed that primary rat hepatocytes maintained in this microperfused culture system exhibit greater retention of drug-metabolizing activity at basal and induced levels than do cells maintained in conventional culture, consistent with the additional finding that more global transcription factor regulators of liver-specific gene expression are also maintained at higher levels, even when the initial cell population is relatively enriched in hepatocytes (and relatively depleted in non-parenchymal cells) compared to in vivo liver. We have extended the culture system to a multi-well plate format that is driven by microfluidics, allowing higher throughput assays useful for both pharmaceutical drug development and basic analysis of liver physiology. This talk will include analysis of the role of non-parenchymal cells on tissue physiology, and application to pharmaceutical toxicology.