The author investigated from various angles behaviours of bone marrow of rabbits in acute bleeding anemia by bone marrow tissue culture. After acute bleeding of 20 cc./kg. of each rabbit, the recovery mechanism in the bone marrow has been compared with that of the normal rabbits by measuring the relative growth rate and the index of cellular density of the bone marrow in hanging drop culture at intervals of 1, 3, 5, 8, 12 and 24 hours as well as 2, 3, 5, 7, 10, 14 and 28 days after bleeding. It has been found that the growth area begins to decrease inmmediately after bleeding and shows the minimum value 5 hours after bleeding, but 12 hours afterwards it starts increasing and relative growth rate 24 hours after bleeding has increased 1.80 times that of the control; 2 days later 2.03 times; 3 days afterwards 2.29 times; 5 days later 2.37 times; and the maximum of accerelation of bone marrow mechanism has been found around 3-5 days after bleeding. The growth rate, which thus reaches the maximum 5 days after bleeding, begins to decrease thereafter and becomes nearly equal with that of the normal rabbits around 10-14 days afterwards.