The Long-Evans Cinnamon (LEC) rat is known to develop hepatitis and liver cancer spontaneously, phenomena attributed to abnormal copper metabolism. This mutant strain of rat shows some clinical features that are similar to those of Wilson's disease, including excessive copper in the liver, reduced excretion of copper into bile, a reduced level of serum copper and a remarkable decrease in serum ceruloplasmin activity. Molecular studies have revealed that the copper transporting P-type ATPase, atp7b, which is the rat gene homologous to human ATP7B, was found to be defective in the LEC rat. These observations have confirmed that the LEC rat is a rodent model for Wilson's disease. In addition, recent studies have suggested that the ATP7B protein is involved in the intracellular transport of hepatic copper. The absence or diminution of ATP7B function results in abnormal copper metabolism in the LEC rat and in patients with Wilson's disease.