The use of tissue cultures as a research tool to investigate the pathophysiological bases of diseases has become essential in the current ag of molecular biomedical research. Although it will always be necessary to translate and validate the observations seen in vitro to the patient or animal, the ability to investigate the role(s) of individual variables free from confounders is paramount toward increasing our understanding of the physiology and their role in disease. Additionally, it is not feasible to conduct certain research in humans because of ethical constraints, yet investigators may still be interested in the physiological response in human tissues; in vitro characterization of human tissue is an acceptable choice. Tissue culture techniques have been utilized extensively to investigate questions pertaining to physiology and disease. The isolation and propagation of human epithelial cells has allowed investigators to begin to characterize the interactions and reactions that occur in response to various stimuli. Moreover, the culture of other human tissue has allowed researchers to investigate pathological cascades as well as other physiological responses. Combining cultured endothelial cells and leukocytes together in vitro under laminar flow conditions has helped elucidate the critical interactions that occur in rolling and emigration of leukocytes during the inflammatory response. Cultured embryonic stem cells that had been subjected to various growth conditions have advanced our understanding of cellular differentiation and growth.