Dose-response curves of Ba/F3 cell clones. 5 × 10⁴ cells were washed three times in PBS and starved for 6 hours in RPMI 1640 medium containing 10% FCS, and then stimulated with the indicated concentrations of Epo (A), GM-CSF (B), IL-5 (C). After 60 hours, XTT was added and the absorbance at 450 nm determined. RPMI medium was used as a blank. Each experiment was done in triplicates; values shown are means. Identical curves were observed in two other independent experiments.