By suspending slices of bone marrow tissue of normal rabbit obtained from the femur in such solutions as Ringer's solution, Tyrode's solution or physiological saline solution, at pH 6.3, 6.8, 7.1, 7.4, 7.7 and 8.0, and by measuring oxygen consumption, the author studied the effect of suspension solutions on the respiration of the bone marrow. The results are as follows: 1. In Ringer's solution Q(o2) was highest, and stochastically there was significant difference in Q(o2) values in the case of the Tyrode's or the physiological saline solution. 2. The decreasing tendency in the oxygen consumption with lapse of time in the course of measuring was least in Ringer's solution, and likewise the variations in the average values of the maximum and the minimum Q(o2) were least in Ringer's solution. 3. As for the physiological saline solution at various ranges of pH, Q(o2) showed the greatest value at pH 7.4. Although there was no significant difference between the value at pH 7.4 and that at pH 7.1 stochastically, but there was significant difference between the value at pH 7.4 and those of other pH. Namely, pH 7.4 as the starting point, if the concentration leans either to acidic side or to alkaline side, Q(o2) tends to decrease, and moreover, the inhibition of Q(o2) is somewhat stronger on the acidic side than on the alkaline side. 4. In the physiological saline solution at various ranges of pH, the decreasing tendency of Q(o2) with the lapse of time is least at pH 7.1 ; and the rate of variations in the averages of the maximum and the minimum oxygen consumption is least at pH 7.7 ; and as the pH turns to more to alkaline side from this pH the decreasing tendency of Q(o2) is marked and also the increase in the rate of variation can be observed. In other words, for the determination of the respiration in bone marrow Ringer's solution is the most suitable one as the suspension solution; and it seems that the phosphate contained in the solution acts as to inhibit the respiration of bone marrow. And the optimal pH seems to lie in between pH 7.1 and pH 7.7 with pH 7.4 as an anchor concentration. Outside this range of pH the respiration of bone marrow is inhibited from the beginning and also the oxygen consumption decreases gradually along with the lapse of time.