Disorders of copper storage are usually treated by chelation therapy. It is generally thought that the chelators act by mobilizing copper from the liver, hence allowing excretion in the urine. This paper has examined the effect of chelators on copper uptake and storage in mouse hepatocytes. Penicillamine, a clinically important chelator, does not block the uptake of copper or remove copper from hepatocytes. Two other copper chelators, sar and diamsar, which form very stable and kinetically inert Cu2+ complexes by encapsulating the metal ion in an organic cage, were shown to block copper accumulation by the cells and to remove up to 80% of cell-associated copper. They also removed most (approximately 80%) of the 64Cu accumulated by the cells in 30 min, but released only a small percentage (less than 20%) of that accumulated over 18 h. The results show that copper in the hepatocyte can be divided into at least two pools, an easily accessible one, and another, not removable even after long-term incubation with any of the chelators. Most of the copper normally found in the cell appeared to be associated with the former pool.