Measurement of 2° CFC frequencies (per 10⁵ cells) from a series of paired BM MNCs and CD34-enriched cell samples. Both MNCs and CD34-enriched cells were plated at densities to give 1,000 and 2,500 CD34⁺lin⁻ cells per well. Each point represents the mean 2° CFC frequency (±SEM) from three to six replicate cultures, and lines connect the points performed with the same cells. Paired CD34-enriched cells and MNCs obtained from the same BM sample are indicated by use of the same plot symbol.