The present disclosure provides a method of determining the frequency and proliferative potential of progenitor cells in a starting cell preparation comprising (a) culturing the cell preparation for 5-10 days in a culture medium comprising FLT-3 Ligand (FL) and Thrombopoietin (TPO); (b) detecting and enumerating the colonies; and (c) assessing the frequency and proliferative potential of progenitor cells in the starting cell preparation based on the number of colonies in step (b). The number of colonies in step (b) correlates to the number of colonies in a standard 14-day colony-forming cell assay. The method is particularly useful for predicting and evaluating the suitability of grafts for transplantation.