SUMMARYThe renal blood flow in seven unselected anaesthetized dogs was calculated on the basis of the disappearance of ¹³¹I-Hippuran from the plasma after a single intravenous injection. The disappearance curve was determined by serial arterial blood sampling as well as by an external counter placed over the heart. A good agreement was found between these methods analyzing the curve either as a single or double exponential function. When the 131I-Hippuran clearance values were corrected for the incomplete renal extraction of Hippuran, they agreed well with the renal blood flow values simultaneously obtained with an indicator dilution technique using indocyanine green dye. An excellent correlation between the renal blood flow measured by the dye dilution technique and the electromagnetic flowmeter in five separate experiments confirmed the reliability in our hands of the dye dilution method. From the results presented in this study it would appear that the single-shot urineless technique described in this paper is a simple and reliable method particularly suitable for the estimation of renal blood flow during anaesthesia.