Purity >95% as determined by SDS-PAGE. Stem cell factor (SCF) is a cytokine made by fibroblasts and endothelial cells. SCF binds to the receptor c-Kit/CD117 and plays a critical role in the maintenance, survival, and differentiation of hematopoietic stem cells. Human SCF shows no activity on murine cells, but murine and rat SCF are active on human cells.