Early relapse of acute lymphoblastic leukemia is not predictable by serial biochemical assays of terminal transferase activity in cells from peripheral blood.

Serial samples of peripheral blood were collected from 37 children with acute lymphoblastic leukemia (ALL) in remission. Activity of terminal transferase (TdT) was assayed by a biochemical technique. False positive results were obtained infrequently (approx. 1%), in contrast to experience with bone marrow analyses. However, early relapse of disease was not predictable in ALL by repeated measurement of TdT in circulating mononuclear cells during remission.