The Native Environment (NE) proliferation assays are performed for those compounds in which cell cycle arrest is suspected to be more relevant than depletion. The drug effect is measured on both the proliferating and nonproliferating cell subsets. For cell proliferation analysis, CFDA staining in conjunction with the immunophenotype allow the analysis of both viability (Annexin-V negative) and proliferation (CFDA peaks) of the blast cells.