Five patients with acute viral hepatitis developed severe intrasvascular haemolysis and unusually high levels of serum bilirubin (427 to 1368 mumol/l). All 5 had high fever, marked anaemia, reticulocytosis and neutrophilic leucocytosis. Three of them developed acute renal failure, which was of non-oliguric type in 2. The clinical course was protracted, but complete recovery occurred in 4 patients between 4 to 10 weeks. One patient with hepatic coma and oliguric renal failure died. Deficiency of the enzyme G-6-PD was confirmed in 4 cases. Massive haemolysis in the patients was probably induced by the administration of chloroquine and other drugs. Intravascular haemolysis should be suspected in patients with acute viral hepatitis, if they show unexplained anaemia and very high serum bilirubin levels, and measures to prevent renal failure should be instituted in such cases.