The preparation technique for 99m-Tc-DTPA(Sn)-complex has been studied in detail in order to find the optimal conditions for preparation. The concentration of DTPA should be at least 10 mM, and that of Sn(II) less than 1 mM, in order to obtain a reproducible high-labelling yield. A dry sterile kit was prepared of 39.3 mg H-5DTPA and 2.3 mg SnCl-2 with 2H-2O in a 10 ml vial. The 99m-Tc-DTPA(Sn) was prepared by adding the 99m-Tc-eluate to the vial. After 1 min the solution was sterile-filtered and was ready for use. The plasma clearance of 99m-Tc-DTPA(Sn) in man determined by blood-sampling up to 200 minutes after administration shows a good correlation to endogenous creatinine clearance (r plus 0.93). The plasma disappearance curve studied during 24 h is, however, a sum of three exponentials corresponding to biological half-times of 18 plus or minus 8 min, 105 plus or minus 9 min and 17 plus or minus 4 h. The slow third component representing about 2% is assumed to be due to binding of 99m-Tc to plasma proteins. The absorbed radiation dose calculated for whole body is 8 mrad/mCi, kidneys 50 mrad/mCi, bladder 300 mrad/mCi, ovaries 17 mrad/mCi and testes 11 mrad/mCi. This agent is a valuable radiopharmaceutical for renovascular clinical problems. Scintigraphic imaging of the aorta, kidneys, ureters and bladder (for residual urinary volume-determination) could be performed.