The generally used MTS-based assay is compared with a bioassay employing a water-soluble tetrazolium dye, WST-8, using NFS-60 cells at a concentration of 7×10 ⁵ cells/mL against 800 IU/mL of PEGylated G-CSF at 24, 48, 72, and 72 h time points to determine the efficacy of PEGylated G-CSF. Further, the optimized WST-8 dye-based assay is used to test the potency of various commercially available PEGylated G-CSF preparations. The results demonstrate enhanced sensitivity of the WST-8-based assay over the conventional MTS-based assay for determining the potency of PEGylated G-CSF using the NFS-60 cell line.