CFU-GM numbers derived from long-term culture nonadherent cells, plated weekly in short-term clonogenic assays (means ± SEM). Normal CD34⁺ cells from healthy controls were plated over stroma of either SD patients (N/SD) or normal donors (N/N); SD CD34⁺ cells were plated over either SD (SD/SD) or normal (SD/N) stroma.