Tissue distribution data obtained in nine normal volunteers were used to estimate the radiation dose to humans after intravenous administration of 99mTc-teboroxime (Cardiotec). Organ uptake as percent of injected dose was measured using quantitative SPECT. Non-linear regression analysis was performed on the organ time-activity data using SYSTAT software. Cumulative activities in these organs were determined by calculating the area under the respective curves after accounting for the physical decay of the radionuclide. The absorbed dose to individual organs was estimated using the MIRDOSE 2 program. The gallbladder and the upper large intestine (ULI) are the target organs and will receive respectively 26.5 and 33.2 muGy/MBq (98 and 123 mrad/mCi) 99mTc-teboroxime under the assumption that the gallbladder empties every 6 hr. The dose to the gallbladder decreases at shorter emptying intervals; with intervals of 3, 4, and 5 hr, the respective doses to the gallbladder are 18.2, 21.0 and 23.7 muGy/MBq (67.4, 77.8, and 87.9 mrad/mCi) 99mTc-teboroxime. However, the dose to ULI remains almost constant at 123 mrad/mCi and will be the limiting factor.