The experiments were carried out with leukemic cells of transmission Line I as well as with Line M-liver. About 50 per cent of the Storrs-Little mice were killed by each line of cells at this time, while 100 per cent of the C58 mice were killed.

2. The normal lymphoid tissues of the two strains of mice were significantly the same in regard to rates of oxygen consumption and both aerobic and anaerobic glycolysis.

3. Leukemic cells of Line I, growing in hosts of Strain Storrs-Little, gave significantly lower rates of aerobic and anaerobic glycolysis than when growing in hosts of Strain C58. Oxygen consumption was significantly higher. Leukemic cells of Line M-liver, growing in hosts of Strain Storrs-Little, gave significantly lower rates of aerobic and anaerobic glycolysis than when growing in Strain C58. Oxygen consumption was not significantly different.

4. After one to three passages through hosts of Strain Storrs-Little, the cell lines were returned to hosts of Strain C58, with immediate return to significantly the same metabolic rates originally given by each line in hosts of Strain C58.

5. These results lead to the more general conclusions that: (a) The genetic constitution of the host modifies the metabolism of the cell line. (b) The same host constitution may modify the metabolism of different cell lines in different ways. (c) Host constitution does not appear to modify the inherent constitution of the leukemic cells, but acts as a determining environmental factor on their metabolism.