In 43 patients with leukemia, we determined the increase of tissue fac
tor (TF) activity production by leukemic cells that was induced by inc
ubation with endotoxin at the time of admission. Definite disseminated
intravascular coagulation (DIC) developed in 8 patients on admission
(Group III) and in 8 patients just after the initiation of treatment (
Group II), but not in the remaining 27 patients (Group I). TF activity
before incubation (TF1) was 0.70 U/10(8) cells or more in 6 patients
of Group III, while it was less in all the patients of Group II and 25
of the 27 patients of Group I. On the other hand, TF activity after i
ncubation with endotoxin (TF2) increased to more than 1.11 U/10(8) cel
ls in all the patients of Groups II and III, while it remained less in
all the patients of Group I. These results suggest that the leukemic
cells in Group II might not have expressed sufficient TF activity to c
ause DIC until chemotherapy was begun, and that 1.11 U/10(8) cells or
more of TF2 might strongly indicate the development of DIC during trea
tment for leukemia.