Vectorial movement of ions and water across polarized renal epithelia is essential for maintaining homeostasis of body chemistries in the face of fluctuating electrolyte intake and losses. Our laboratory studies epithelial ion transport in the Drosophila melanogaster renal epithelium, the Malpighian tubule. We study ion channels and transporters, and the signaling pathways regulating them. We have also been investigating the role of the septate (occluding) junction protein, Mesh, first identified by Professor Furuse, in the Malpighian tubule. I will discuss recent results on ion transport through basolaterally localized ion transporters and channels, as well as our findings on the role of Mesh in epithelial structure and function in developing and adult tubules.