The absorption by muscle, fat lung, compact bone, and spongy bone of beef was measured for roentgen ray generators of 100 kv (hvl 1 mm Al), for 200 kv (0.9 mm Cu), 400 kv (4.9 mm Cu), and gamma radiation of Co60. The results are presented in diagrams. There is little change in the differential absorption between muscle and tissues between 400 and 1,250 kv. Below 200 kv the absorption in bone and lung increases faster than the absorption in muscle. The absorption in fat increases more slowly than that in muscle. Since the absorption in lung is about 1/3 that in muscle, ordinary depth dose values do not hold for treating lung lesions.