Proliferative response of CFU-GM (A) and BFU-E (B) derived from highly purified PB and steady-state BM CD34⁺ cells to recombinant human growth factors. The results are expressed as the mean ± SEM of the fold increase compared with PHA-LCM–supplemented cultures. The clonogenic efficiency of control (PHA-LCM) dishes was 1.4% ± 0.3% (CFU-GM) and 2.5% ± 0.5% (BFU-E) for PB CD34⁺ cells and 1.4% ± 0.4% (CFU-GM) and 2.2% ± 0.3% (BFU-E) for BM CD34⁺ cells, respectively (P < .5). All of the experiments were performed in the presence of 2 U/mL of Epo. *Statistically significant.