Immortalized cell lines derived from embryonic mouse kidneys are useful tools for exploring signaling pathways, morphogenetic mechanisms, and gene function in renal development: they also provide a means for efficient first-round screening of panels of small molecules intended to combat renal pathologies such as the development of cysts, and such cell line-based screening can allow a valuable reduction in the numbers of animals needed for a given line of research. This chapter presents a simple method for generating cell lines from the "Immortomouse," which carries a temperature-sensitive SV40 antigen, under the control of an interferon-regulated promoter.