Eleven Bedlington terriers were found to have a mean hepatic copper concentration of 6,321 micrograms/g dry wt (normal, 200 micrograms/g dry wt) and renal copper concentration that was three or four times normal. Brain copper levels were normal in younger dogs, were elevated in two older dogs, and were 100 times normal in one dog that died of the disease. Increased concentrations of copper in the liver, kidney, and brain also characterize Wilson's disease. Erythrocyte survival was normal in three affected dogs, but serum glutamic-pyruvic transaminase levels were usually elevated. Unlike the hypoceruloplasminemia of patients with Wilson's disease, plasma ceruloplasmin activity was not only normal but was also slightly elevated in the terriers. Despite their normal or excessive ceruloplasmin, the Bedlington terriers could convert ionic 64Cu to radioceruloplasmin but did so only very slowly. These dogs accumulated significantly more 64Cu in their livers than normal, much like patients with Wilson's disease do before symptoms develop.