From 1976 to 1985, a total of 58 infants and children with the hemolytic-uremic syndrome were randomly assigned to treatment either with heparin and dipyridamole or with supportive management only. In the treatment group, two patients died in the early weeks of the disease. Analysis of clinical and laboratory data showed no significant difference between either group of patients as to the evolution of their illness except for a significantly higher incidence of anuria and a significantly faster recovery from hypertension in the treated group. Renal biopsy studies showed no differences between the two groups in terms of incidence and severity of the histologic lesions. The long-term data on blood pressure and creatinine clearance values in the survivors were similar in both groups. This study indicates that treatment with heparin and dipyridamole has no benefit over symptomatic therapy alone in the typical form of childhood hemolytic-uremic syndrome.