Fms expression was measured by Northern blot analysis in the pretherapy leukemia cells of 30 patients with acute myelogenous leukemia (AML) who either entered CR or who were shown to have drug resistant disease. High levels of fms expression correlated with a CR outcome and were strongly associated with the fall in the number of leukemia cells during the first six days of remission induction therapy. In contrast, similar studies of myc expression failed to demonstrate any relationship to treatment outcome. Considering those genes whose expression have been measured to date, the level of expression of fms is the one which is most highly correlated with treatment outcome in AML. No significant relationship between the expression levels of these two genes and the cell cycle characteristics of leukemia cells in vivo were detected.