The relation between the characteristic variations of the serum protease inhibitors and clinical course were examined in patients with various blood diseases.Materials and Methods;Sixty-nine patients with various blood diseases (25 patients of AML, 4 of ALL, 11 of CML, 4 of APLA, 18 of iron dificiency anemia (IDA) and 7 of ITP were selected in this study. Thirty control normal subjects were also picked out. Serum protease inhibitors were measured by use of the single radial immunodiffusion method. Alpha1-antitrypsin (α1AT), α2-macroglobulin (α2M), inter-α-trypsin inhibitor (IαI), α1-antichymotrypsin (α1X), antithrombin III (AT-III) and plasminogen (PLg) were respectively determined in this examination.Results and Conclusions;The serum protease inhibitors in the blood diseases were compared with those in the normal subjects. Normal levels were shown as follows.Alpha1AT; 251±22mg/dl, α2M; 213±47mg/dl, IαI; 58±5mg/dl, α1X; 45±5mg/dl, AT-III; 23±4mg/dl and PLg; 14±2mg/dl.Alpha1 AT and α1X markedly increased, α2M, IαI and PLg decreased in AML and ALL.Alpha1 AT and AT-III increased in CML. Alpha1 AT, α1X and AT-III significantly increased in APLA. Alpha2M and α1X increased, PLg decreased in ITP. Alpha2M markedly increased in IDA. When the patients with leukemia changed to remission stage from acute stage, serum α1AT and α1X elevating in acute stage decreased, on the other hand serum IαI and α2M transfered to normal range from low level. In the complete remission stage of the clinical course, the α1AT and α1X levels returned to the normal levels but α2M, IαI and PLg continued slightly elevated in AML.It was suggested that these hematologic findings would be available as indication of prognosis and therapeutic effect in various blood diseases.