Sensitivity to araC of acute leukemia cell lines and fresh blasts from patients. Cells were incubated for 72 hours in culture media containing graded concentrations of araC. After the incubation period, cell viability was determined by the MTT assay. The data are mean ± SEM of 12 replicate measurements at each araC concentration. IC₅₀ values were 980 pmol/L (CEM), 5.2 nmol/L (OCI/AML-2), 8.2 nmol/L (AML patient H.M.), and 72 nmol/L (ALL patient T.Z.).