In 31 patients with renal carcinoma referred for angiography, rapid sequence angiography was performed in 25. In 18 of the patients determination of renal blood flow and related parameters was made in conjunction with the angiography. Carcinomas with high and medium-high differentiation comprised Group I, while those with medium and poor differentiation constituted Group II. In both groups a positive correlation was demonstrated between the renal blood flow and the tumour area. In group I, positive correlation (t greater than 2) was demonstrated between the vascular volume and the tumour area, between the vascular resistance and the emptying time of the tumour arteries and the normal renal arteries. There was some degree of shunting of blood in all tumours. Comparison of the arterial emptying time of the tumour arteries with the parenchymal arteries does not allow of staging of renal carcinomas. The degree of shunting may be an indication of the degree of malignancy and poor differentiation.