Recombinant human VEGF121 (HZ-1204) induces dose-dependent proliferation of the HUVEC (human umbilical vein endothelial) cell line. Cell number was quantitatively assessed by PrestoBlue® cell viability reagent. HUVEC cells were treated with increasing concentrations of recombinant VEGF121 for 96 hours. The EC50 was determined using a 4-parameter non-linear regression model. Activity determination was conducted in triplicate on a validated bioassay. The EC50 range is less than 15 ng/mL.