Concentrations of leukocyte elastase (ELP) and cathepsin G (CLP) in leukocytes, plasma and serum from healthy human blood were measured using synthetic substrates. The best condition of the extraction of both enzymes from leukocytes was first studied, and the normal values of ELP and CLP in plasma and serum were calculated from the decreased ratio of their activities after the addition of plasma and serum to the pure enzymes. The results obtained were as follows; 1) The amidolytic activity of ELP which obtained by repeated freezing and thawing twenty times in Tris-HCl buffer (containing 0.15-2.0M NaCl) showed similar value to the activity extracted with 2M NaClO4. The amidolytic activity of CLP weakened rapidly in the medium, while the extraction of maximum activity was obtained by repeated freezing and thawing in the above mentioned buffer. 2) The amidolytic activities of ELP and CLP were decreased to 4% and 45%, respectively, by the addition of normal plasma or serum. 3) Normal values obtained were as follows. ELP and CLP were 7.5±1.9μg and 6.0±1.7μg per 107 leukocytes, respectively. ELP and CLP in plasma were 150±66ng/ml and 13±4.4ng/ml, and those in serum were 315±165ng/ml and 26±9.8ng/ml, respectively.
