To assess the contribution of hepatitis C virus to non-A, non-B fulminant hepatitis in Japan, we compared 10 major clinical features among 7 patients with type B fulminant hepatitis (type B group), 13 patients with non-A, non-B fulminant hepatitis with evidence of hepatitis C virus infection (type C group) and 10 patients without evidence of hepatitis C virus infection (NANB group). Duration from first symptom to coma and that from onset of jaundice to coma was significantly longer in the type C group (median = 39 and 25 days, respectively) and in the non-A, non-B group (median = 29 and 12 days, respectively) than in the type B group (median = 9 and 2 days, respectively) (p < 0.01). The maximum median AST level was significantly lower in the type C (1,689 U/L) and non-A, non-B groups (1,353 U/L) than in the type B group (5,780 U/L) (p < 0.05). Serum transaminase levels showed a single peak in six of seven of the type B patients, whereas they formed two or more peaks in all of the type C patients and in most of the non-A, non-B group (p < 0.05). Six of seven in the type B group, 6 of 13 in the type C group and 4 of 10 in the non-A, non-B group survived (p < 0.05). We found no significant difference in any of the 10 clinical features between the type C and non-A, non-B groups.(ABSTRACT TRUNCATED AT 250 WORDS)