Serial coagulation investigations were performed in 4 children with the haemolytic uraemic syndrome treated with heparin by continuous infusion. 2 anuric patients showed consumption of factor V and fibrinogen early in the disease, with thrombocytopenia and raised fibrin degradation products. These changes regressed during heparin therapy and renal function fully recovered in both patients. A third patient with a mild form of the disease, normal urinary output, and only borderline thrombocytopenia did not develop demonstrable depletion of factor V or fibrinogen. In a further patient a secondary `wave' of consumption of platelets and perhaps fibrinogen was seen late in the course of the disease. These findings confirmed the occurrence of a consumptive coagulopathy in severe cases of haemolytic uraemic syndrome.