Individual kidney glomerular filtration rate (IKGFR) can be measured from the renogram from the rate of uptake of technetium-99m diethylene triamine penta-acetic acid (99mTc-DTPA). A blood sample is required to derive IKGFR in millilitres per minute, which is then usually normalised to body surface area. We describe a technique which does not require a blood sample, is already normalised for plasma volume and uses the robust Patlak plot for measuring renal uptake. The rate of kidney uptake, dR(t)/dt, at time = 0, as a fraction of the injected dose, is equal to the fraction of the plasma volume (PV) filtered per minute, i.e. IKGFR/PV. The gradient dR(0)/dt cannot be accurately measured directly but is equal to [alpha .LV(0)], where alpha is the renal uptake constant (proportional to IKGFR) and LV is the count rate over a left ventricular ROI. LV(0) was obtained by extrapolation of LV(t), while alpha is the slope of the Patlak plot up to 3 min. GFR/PV (i.e. right plus left kidneys) in patients with normal renal function was about 0.04 min-1, as would be expected from normal values of GFR (120 ml/min) and plasma volume (3 l). GFR/PV correlated significantly with the ratio of GFR to extracellular fluid volume (ECV), measured from the terminal exponential of the plasma clearance curve (GFR/PV = 3.2.GFR/ECV + 5.3 ml/min/l [r = 0.82, n = 82]). GFR/PV (r = 0.74) and GFR/ECV (r = 0.82) both correlated inversely and non-linearly with plasma creatinine in 43 studies where the measurement was made within 1 week of the 99mTe-DTPA study.(ABSTRACT TRUNCATED AT 250 WORDS)