Mean (±SEM) concentrations of AG957 inducing 50% inhibition (ID₅₀) of CML (▪) and normal (□) colony formation. ID₅₀ values were calculated for each experiment by extrapolating from a least square linear regression line relating AG957 concentration to the percentage of colony growth inhibition. *Statistically significant (P = .004, at least) when compared with normal samples (Student’s t-test for unpaired data).