An attempt was made to improve renal function in five patients with malignant hypertension and progressive renal disease by treatment with intravenous heparin. Oral dipyridamole, an antithrombic agent, was given in four patients. The renal disease was far advanced in four of the five, but only one patient had evidence of a microangiopathic hemolytic anemia. Although there was an apparent beneficial effect of heparin and dipyridamole on the microangiopathic hemolytic process, no beneficial effect of therapy on the renal function of any of the five patients was documented.