The development of hypertension after kidney transplantation was examined in a consecutive series of 83 transplantations (79 patients) with a graft survival of more than 30 days. After transplantation, 50% of the normotensive recipients developed mild or severe hypertension, while 74% of the hypertensive recipients remained hypertensive. Stenosis of the graft artery with a narrowing of the diameter of more than 50% was found in 13 patients and in 3 patients a minor or peripheral stenosis was found. Significantly more stenoses were seen in the presence of two donor arteries, whereas no other etiological factors could be shown. In arterial stenosis, severe hypertension was established within a few months after transplantation, but in spite of satisfactory controlled blood pressure and good graft function, hypertensive crises could arise. It is therefore concluded that arteriography and renin analysis should be considered in all cases of severe hypertension, and surgical correction should be considered when arterial stenosis is present.