Two renal transplant patients developed anemia during treatment of hypertension with enalapril medication. Hemoglobin levels normalized after administration of enalapril was stopped. In one patient, it was demonstrated that the discontinuation of enalapril was followed by a decrease in renal blood flow and a significant increase in the plasma erythropoietin levels that preceded the rise in hemoglobin. These observations are consistent with the hypothesis that angiotensin-converting enzyme inhibition may cause anemia by increasing renal blood flow and consequently decreasing erythropoietin levels.