In 80 mass lesions of the kidney, we found 11 cases with calcification; six of these occurred amongst 48 tumours and five amongst 32 solitary cysts. In particular, the following were found: 1. The frequency of calcification of 12 to 14% corresponds with that given in the literature. If other radiological signs fail indicate the nature of the space-occupying lesion, then calcification may be of diagnostic value. 2. Calcified cyst walls appear as fine, even, curvi-linear lines, Dense, irregular and extensive calcification indicates a solid tumour. 3. Ring or curvi-linear calcification in not a reliable sign of a cyst. Tumours may also show this type of calcification indicates a solid tumour. 3. Ring or curvi-linear calcification is not a reliable sign of cyst. Tumours may also show this type of calcification. Calcification occurs in solitary cyst with about the same frequency as in tumours. 4. Histologically all calcified tumours were clear cell carcinomas, mostly hypervascular. Only one case showed central necrosis.

1. Renal excretion as seen in the urogram does not parallel changes in blood flow. The significance of the early urogram as a test of function is therefore very limited. 2. Following acute stenosis of one renal artery, there is simultaneous excretion by both kidneys until flow is reduced to 60%; exretion is delayed, with values of 0.5 to 7.5 minutes, following reduction to 30 to 60% of the original; there is no excretion below 30%. 3. Unilateral delay in excretion occurs at about the level of "critical occlusion pressure". 4. Delayed excretion is observed at the level of the so-called "critical stenosis" of the renal artery. A reduction of flow above 20% follows a reduction of the artery in excess of 66%, corresponding with a reduction of the lumen of more than 90%. 5. These findings indicate that delayed excretion in the early urogram is to be expected only as a result of severe stenosis of the renal artery and represents a late feature of renal vascular disease.

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After experimental stenosis of the renal artery of the dog, the isotope nephrogram shows a prolongation of the transit-time, when the renal blood flow is reduced to 40--70%. This finding was most significant in low diuresis (0,05--0,2 ml/min), sporadic in moderate diuresis (0,2--2,0 ml/min), no longer demonstrable in forced diuresis (greater than 2,0 ml/min). The diuretic effect of X-ray contrast medium (70% Na-Meglumin-Jotalamat, 0,5 ml/kg i.v.) normalizes a pathologic ING in low diuresis.