NmU functions to facilitate the production of erythroid progenitors from primary human CD34⁺ cells. Primary human CD34⁺ cells isolated from cord blood were cultured in methylcellulose with (A) EPO and SCF in the absence and presence of NmU to produce BFU-E, (B) EPO without and with NmU to form CFU-E, or (C) IL-3 and GM-CSF in the absence and presence of NmU to yield CFU-GM. The frequencies of CD34⁺-derived BFU-E, CFU-E, and CFU-GM are presented from duplicate determinations from 3 independent experiments. *P < .05.