AB Objectives: The single-sample 99mTc-diethylenetriamine penta-acetate (DTPA) clearance method by Christensen and Groth is recommended by the Radionuclides in Nephrourology Committee on Renal Clearance for use in adults with an estimated glomerular filtration rate (GFR) >=30 ml/min. The purpose of this study was to test a new 99mTc-DTPA single-sample low clearance formula for GFR lesser than 30 ml/min. Methods: Twenty-one adult patients (29 investigations) were included. Reference clearance was calculated with both 51Cr-EDTA and 99mTc-DTPA according to Brochner-Mortensen with samples drawn between 3 and 24 h. Single-sample clearance was calculated from a 24 h sample using the low clearance formula C(t) is the activity of the tracer in the plasma sample t minutes after the injection and Q0 is the injected amount. ECV is the extracellular volume in ml defined as the distribution volume of the tracer. ECV is estimated from the body surface area as ECV=8116.6xbody surface area-28.2. Results: The mean difference between reference and 99mTc-DTPA single-sample clearance was -0.5 ml/min (SD 1.0 ml/min) for 99mTc-DTPA and -0.8 ml/min (SD 1.2 ml/min) for 51Cr-EDTA as reference clearance. Conclusion: In adult patients it is possible, even with GFR lesser than 30 ml/min, to get an accurate determination of 99mTc-DTPA plasma clearance from a single sample using the mean sojourn time approach. The blood sample should be obtained about 24 h after injection of the GFR tracer.