On the basis of a review of 186 cases of carcinoma of the kidney studied by arteriography in the Department of Radiology for Diseases of the Urinary Tract at Necker Hospital, the authors drew the following conclusions: 1. The diagnosis of carcinoma could be affirmed in the very great majority of cases and suspected in the others. 2. There were no instances of a reassuring false diagnosis (cyst). 3. A precise, rigourous and faultless technique, perfectly demonstrating the exteriorised part of the mass and attentive, thorough and careful interpretation of the films obtained, in particular with regard to the mass in its exteriorised portion, are always essential in order to obtain such results. In particular, the presence of a vascularisation of a discontinuous opaque band at the periphery of the mass in its exteriorised part indicates a strong suspicion of a necrotic malignancy and under no circumstances is an unreserved diagnosis of a cyst possible. 4. Diagnostic errors in the sense of false positives involving certain "thick-walled" cysts should be eliminated by pre-operative needle puncture. 5. The authors conclude by describing the method of radiological exploration which they feel to be desirable in practice following the discovery of a renal mass by intravenous pyelography.