The retinal pigment epithelium (RPE) forms the outer blood-retinal barrier and has an intimate structural and functional relationship with the rod and cone photoreceptors. A key function of the RPE is to regulate the photoreceptor microenvironment by transporting solutes, nutrients, and water to and from the choroidal blood supply. Among the host of transport mechanisms in the RPE, none is more important than active Cl- transport, which regulates the hydration of the photoreceptor extracellular space and promotes retinal adhesion. In our patch-clamp studies of freshly isolated mouse RPE cells, we discovered an unusual ion channel in the basolateral membrane that is highly selective for the biologically active anion, thiocyanate (SCN-). Remarkably, this channel yields whole-cell currents in the nanoamp range even when the extracellular SCN- concentration is less than 1 mM. SCN- is of interest because it is present in most extracellular fluids and is known to play key roles in innate immunity, redox regulation, synaptic modulation, and extracellular matrix biology. I will present evidence from a variety of approaches that SLC26A7, an ion channel in the SLC26 transporter family, underlies the SCN--selective conductance in the RPE and discuss how it may participate in Cl- and SCN- transport.