Controlling the extent of cation exchange reactions is a promising route for tuning the material composition and properties of nanostructures. Here we demonstrate how measuring the conductivity of nanowires during cation exchange can be used to monitor the transition from CdSe to Ag(2)Se, in situ. In addition, by imaging the same wire mat region before and after complete cation exchange, we find that the shape and morphology of the nanowires are completely preserved.