U937/STAT5 Reporter (GFP) cells are derived from the human pro-monocytic cell line U937 by stably integration of a STAT5 GFP reporter construct. U937 cells are able to differentiate into either dendritic cells or macrophages, depending on the surrounding signals. U937 cells are widely used for studies of monocyte/macrophage differentiation, the macrophage-tumor cell interaction and anti-cancer drug screening. U937/STAT5 Reporter (GFP) cells stably express GFP under the control of the STAT5 response elements, can be used for monitoring the activity of STAT5 signaling pathway.