Expansion of CFU-GM from CD34⁺ CD38^dim cells and CD34⁺ CD38⁺ cells. Normal marrow MNC were sorted into CD34⁺ CD38^dim and CD34⁺ CD38⁺ fractions and subsequently cultured in liquid medium with 4 different combinations of cytokines. In each trial (n = 5), the number of CFU-GM was assessed at weekly intervals to determine the maximum number produced for each condition. The figure shows average values for CFU-GM input and the maximum number of CFU-GM generated with each of the combinations. [IL-3 + IL-6] could not sustain CFU-GM from the CD34⁺ CD38^dim fraction. [IL-3 + IL-6 + FL] supported a significant expansion of CFU-GM from the CD34⁺ CD38^dim fraction in 3 trials, whereas none were recovered in 2 others. Such variability (also seen in Fig 2) decreased the mean yield to less than that of the CD34⁺ CD38⁺ fraction. The greatest expansion was obtained with [IL-3 + IL-6 + KL + FL]. *CFU-GM yield from CD34⁺ CD38^dim cells in [IL-3 + IL-6 + KL + FL] significantly greater than same cells in [IL-3 + IL-6 + KL] (P = .01). **CFU-GM yield from CD34⁺ CD38^dim cells in [IL-3 + IL-6 + KL + FL] significantly greater than CD34⁺ CD38⁺ yield in same cytokine mix (P = .003). ^#CFU-GM yield from CD34⁺ CD38⁺ cells in [IL-3 + IL-6 + KL + FL] not significantly greater than same cells in [IL-3 + IL-6 + KL] (P = .18). ^##Generation of CFU-GM in the presence of [IL-3 + IL-6 + FL] was not significantly greater in the CD34⁺ CD38⁺ fraction than in the CD34⁺ CD38^dim fraction (P = .30).