Wilson's disease protein (WNDP) is a copper-transporting P(1)-type ATPase which plays a key role in normal distribution of copper in a number of tissues, particularly in the liver and the brain. Copper has numerous effects on WNDP, altering its structure, activity, and intracellular localization. To better understand the function of this copper-transporting ATPase and its regulation by copper, we have recently developed the functional expression systems for WNDP and for Atox1, a cytosolic protein that serves as an intracellular donor of copper for WNDP. Here we summarize the results of our experiments on characterization of the enzymatic properties of WNDP and the effects of Atox1 on the WNDP activity.