1. A new method, based on the transit time of o-iodohippurate sodium (Hippuran) through the kidney, is proposed as an accurate non-invasive means of measuring the intrarenal flow distribution in man.
2. Data from [123I]Hippuran γ-camera renography are utilized in this method which employs region of interest selection, deconvolution, cross-correlation and curve subtraction to obtain the spectrum of transit times through the cortical and juxtamedullary nephrons.
3. In 12 normal subjects the mean percentage cortical flow was 83.9% (sem 0.7%) which is approximately the anatomical proportion of cortical nephrons in the human kidney.
4. Cortical flow as a percentage of total was significantly reduced in 21 hypertensive patients, all of whom had no evidence of primary renal disease (mean 74.6%, sem 1.5%).
5. In both the normotensive and hypertensive groups there was a good correlation between the results obtained from the left and right kidneys of the same patient showing the parallel physiological response of the two kidneys (mean difference 4%, P < 0.001).
6. Reduction in the distribution of flow to the cortical nephrons in the essential hypertensive patients supports the hypothesis that renal autoregulation is important in this syndrome.