Measurement of 2° CFC frequencies (per 10⁵ cells) from a series of paired expanded BM MNCs and CD34-enriched cell samples assayed over a range of plating densities. Each point represents the mean 2° CFC frequency from three to six replicate cultures, and lines connect the points performed with the same cells. Paired MNC and CD34-enriched cells obtained from the same BM sample are indicated by use of the same plot symbol.