Using the concept of effective dose equivalent, HE, it is shown that a knowledge of the detailed biodistribution data in most organs and tissues taking up 99mTc labelled radiopharmaceuticals is unnecessary for the calculation of radiation risk. Reasonably precise dosimetry (+/- 25%) can be obtained from urine excretion data alone providing there is no significant uptake within the gonads or the thyroid. Special attention should only be paid to absorbed dose measurements in red bone marrow, skin, lungs, gonads and thyroid, with the greatest attention directed toward the retention and dosimetric aspects of radioactivity in the latter two organs. An example HE calculation for 99mTc labelled d,1-HMPAO is presented to illustrate the importance of these specific five organs to radiation risk.