IGF-1 is a major mitogen in FCS for Ba/F3-d392 cells. Short-term proliferation assays were performed with Ba/F3-d392 cells stimulated with 100 mU/mL Epo ± 0.2 nmol/L IGF-1, ± 0.2 nmol/L IGF-1 after pretreatment with anti–IGF-1, ± 0.2 nmol/L IGF-1 after pretreatment with control anti-IgG, ± 1% FCS, ± 1% FCS after pretreatment with anti–IGF-1, and ± 1% FCS after pretreatment with control anti-IgG, as described in Materials and Methods. Data points represent the mean ± SE of triplicate determinations.