The alpha-amylase activity has been determined in leukocytes and sera of patients with acute myeloblastic leukemia, chronic myeloid leukemia, chronic lymphoid leukemia and in a control group. The leukocyte alpha-amylase activity was calculated in units per mg of protein. In all groups of patients an increase of the tested enzyme could be observed. The enhancement of alpha-amylase activity was correlated with the rate of leukocytic maturation. The normal activity of this enzyme in the sera of tested patients should be stressed. This statement that seems to be contradictory is briefly discussed.