To the Editor. —It has been brought to our attention that there is incorrect information about Wilson's disease in the new 15th edition of The Merck Manual (pp 947 to 949), particularly regarding diagnosis and treatment. Wilson's disease, transmitted in an autosomal recessive fashion, is always fatal unless it is diagnosed and an appropriate lifelong therapeutic regimen instituted before progressive and irreversible pathology of the liver or brain develops. 1 Concerning diagnosis, a normal ceruloplasmin level is 200 to 500 mg/L (20 to 50 mg/dL) , not 150 to 400 mg/L (15 to 40 mg/dL). A concentration of hepatic copper greater than 250 μg/g dry weight (not >250 μg/g wet weight) is absolutely diagnostic if, and only if, the serum ceruloplasmin concentration is less than 200 mg/L ( 20 mg/dL). Diagnosing Wilson's disease in these patients