A method, introduced by the authors, for assessment of the extent of bone marrow haemopoietic activity in normal subjects is reported. 99mTc-sulfur colloid is injected, and the bone marrow visualized on gamma camera, type Phogamma-HP, which is equipped with 4096 channel analyzer (Nuclear Chicago). By use of a standard and by registering the activity in "zones of interest" from the arm, forearm, thigh and lower leg bones, indices and mean normal values in 26 normal subjects were calculated and reported.