Stat5-deficient BMMCs are defective in IL-3– and SCF-induced survival. Wild-type or Stat5-deficient BMMCs were cultured in the indicated concentrations of IL-3 or SCF for 48 hours. Apoptosis was assessed by the presence of subdiploid DNA after PI-DNA staining. Cells were also cultured in medium alone, or in IL-3 (5 ng/mL) + SCF (50 ng/mL) as death and survival controls, respectively (shown on the right of the graph). Data shown are means and standard errors from 3 to 8 samples per point, taken from 2 of 9 independent experiments. *P< .001; +P < .05 by Student t test or analysis of variance.