The hypernephroid carcinoma is the most common tumour of the kidney in adults. Haematuria can occur, even in the early developmental stages. In investigations of 30 patients with-haematuria, radiological examinations were made and the plasma histamine levels were determined in both from the renal artery and vein, the vena cava and the aorta. After nephrectomy, the histamine content of various tissues in different regions of the kidney were investigated. Significant increases of plasma and tissue histamine levels were found in the veins of the tumour-riddled kidney and in the tissue surrounding the tumour. an experimental study on dogs investigated whether or not an injection of histamine into the renal artery would provoke haematuria. Dose-dependent haematuria occurred, which was most pronounced following intra-arterial injection of 25 micrograms/kg of histamine.