The development of microanalytical methods and the use of technics resulting in leukocyte preparations of satisfactory purity have allowed us to estimate several metabolic functions and to calculate their relative values in different classes of cells. These different categories were analyzed mathematically in the attempt to determine the total enzyme activity of different types of leukocytes.

We have ascertained that the monocyte, derived directly from the reticuloendothelial system, has glycolytic and proteolytic activity, respiration, reducing power, and esterase activity markedly greater than that of the neutrophilic polynuclear. The lymphocyte shows, with exception of the reducing power, low active enzymatic functions in comparison to the neutrophil. The eosinophil, in two pathologic cases, resembles the neutrophil in glycolytic activity, but possesses very low proteolytic capacity and oxygen consumption.

The enzymatic behavior of the leukemic cell shows that the proteolytic power of the myeloblast is diminished while glycolysis and, occasionally, esterase activity, are raised; in the lymphoblast, glycolysis is low, with a slight Pasteur effect. Synthesis of porphobilinogen is intense in the leukocytes, but formation of the porphyrin ring has been observed only in certain cases of leukemia.

A greater number of cases must be examined in order to confirm these preliminary observations on the enzymatic behavior of leukocytes.