Extreme hyperbilirubinemia, massive hemolysis and hepatic encephalopathy were reported in a G6PD-deficient patient with viral hepatitis. Investigation of the G6PD properties revealed that this patient's enzyme represented a hitherto undescribed variant (Bnei Brak), characterized by heat stability and a unique triphasic pH-related enzyme activity curve. It is possible that the marked hemolytic process in this patient was enhanced by a further decrease in the activity of the already deficient enzyme during acidosis.