A method for determination of the transferase activity of 1-asparaginase in presence of hydroxylamine is developed. The optimally determined quantity of the enzyme was from 0.7 to 20 i. u. The conditions optimal for the enzymatic reaction and for quantitative estimation of 1-aspartyl-beta-hydroxamic acid were studied. The transferase and hydrolase activities of 1-asparaginase from E. coli were compared. The enzyme catalyzed at equal rates hydrolysis and hydroxylaminolysis of 1-asparagine.