Serum, urine and tissue biochemical findings were studied in 21 cases of fulminant Wilson's disease with respect to the value of a recently described biochemical index based on serum alkaline phosphatase and total serum bilirubin levels, and these cases were compared with 193 other cases of fulminant liver failure. Serum bilirubin, alkaline phosphatase and AST levels found in fulminant Wilson's disease were significantly different from those found in other cases of fulminant liver failure, but differentiation from other causes of fulminant liver failure on the basis of these biochemical parameters was not possible. The alkaline phosphatase/bilirubin and aspartate AST/bilirubin ratios derived from the above parameters were also significantly lower in fulminant Wilson's disease than in other categories of fulminant liver failure, but distinction between diagnostic categories on this basis was not possible. When ratios that correctly identified all cases of fulminant Wilson's disease were selected, 59/190 (31%) and 84/190 (44%) cases of non-Wilsonian fulminant liver failure would erroneously be assigned a diagnosis of fulminant Wilson's disease, by alkaline phosphatase/bilirubin and AST/bilirubin ratios, respectively. A low alkaline phosphatase-to-bilirubin ratio (< 0.57) in any category of fulminant liver failure suggested a significantly worse prognosis than in cases with higher ratios (chi 2, Yates' corrected = 5.37, p = 0.02). In the Wilson's disease group, serum and hepatic copper and ceruloplasmin concentrations were normal in 4/21, 2/15 and 2/19, respectively, whereas urinary copper level was elevated in 18/18 and was the most valuable test in diagnosis.(ABSTRACT TRUNCATED AT 250 WORDS)