This chapter describes a technique by which an epithelial cell line can be used for expression experiments. Basically, cells are harvested from a subconfluent monolayer and fused to form giant cells. For expression experiments the giant cells have to be identified first, then injected individually, and, finally, 24 hr after microinjection, re identified to perform the electrical analysis. After injection the cells are documented in terms of their location and the amount of injected mRNA so that the injected cells can be identified individually after 24 hr. After injection the Ringer solution is exchanged by culture medium (plus antibiotics) and the injected cells are incubated for expression. About 24 hr after mRNA injection the injected cells are studied by electrophysiological techniques. Intracellular cell membrane and specific plasma membrane resistances of fused Madin-Darby Canine Kidney Cells (MDCK) cells are measured according to techniques described in this chapter.