Bile acid levels were measured in the sera, cerebrospinal fluid (CSF), and brain tissue of 10 patients immediately after death from fulminant hepatic (FHF). Serum bile acids in FHF were predominantly conjugated, and total bile acid levels were higher in all 10 patients than in normal controls (85.9 +/- SE 8.4 compared with 5.7 +/- 0.4 nmol/ml, P less than 0.001). Small but significant amounts could be detected in CSF (range 1.2-5.3 nmol total bile acid/ml) and brain biopsies (1.0-18.8 nmol/g wet weight) of FHF patients, whereas none could be detected in CSF and brain biopsies of patients dying without evidence of liver disease. There was no relationship between serum, CSF, or brain levels and duration of coma, or presence of cerebral oedema found in five FHF patients at necropsy. However, serum bile acid levels were similar in FHF to those found in chronic liver disease without encephalopathy and lower than those found to inhibit brain respiration in vitro. A primary role for these compounds in the pathogenesis of coma in FHF therefore seems unlikely.