Bone marrow CD34⁺ cells and GM-CFU 2 and 3 weeks after 5 Gy TBI, respectively (arithmetic mean ± SE). Since the variance of this type of datum is inevitably large due to variations of bone marrow content at the puncture site and admixture with peripheral blood cells, in addition to possible variations in radiation sensitivity and exponential reconstitution, the other groups did not show significant differences versus the placebo controls.