The anomalies caused by the injection of contrast medium were studied in animal experiments with dogs on 53 kidneys, and on clinical material, via the renal angiograms of 130 patients. In these trials vascular spasms were seen or, alternatively, filling defects in the parenchyma. Both were using the classical tri-iodated contrast medium iodamide and the monoacid dimeric contrast medium with low osmotic pressure (Hexabrix); in several cases, histological changes (for example, necroses of the tubular epithelium) were seen. Anomalous angiograms were also seen in the human experiments, especially in case of incorporation of large quantities of contrast medium and selective use of a thick catheter. Anomalies were more likely to occur in kidneys with diseased parenchyma.