Stimulation of CFU-GM growth is inhibited by antibodies against G-CSF and IL-6. A total of 2,000 DR⁺ cells/well were plated in methylcellulose cultures supplemented with either 5 ng/mL IL-3 alone or conditioned medium from irradiated human stroma (final concentration 50%). All cultures were supplemented with 3 IU/mL recombinant EPO. Neutralizing antibodies against human G-CSF, human IL-6, or normal goat IgG were added on days 0, 4, 7, and 11 to the indicated wells, which were supplemented with stroma conditioned medium. N = 4. Comparison between stroma CM or goat IgG and other conditions: *P < .05.