Increased utilization of the granulocyte-macrophage colony-forming unit (CFU-GM) assay for quality control, dosing, and clinical investigation of peripheral blood (PB) stem cell and bone marrow (BM) products led us to compare two commercially available media ("Ready-Mix" [RM] from Terry Fox, Vancouver, Canada and Stem Cell CFU Kit [SCCK]) from GIBCO, Grand Island, NY-Baxter Healthcare Corp., Deerfield, IL) to our standard laboratory media (SLM). Aliquots of mononuclear cells (MNC) from PB and BM donors were cultured in triplicate in the three media and CFU-GM and erythroid burst-forming units (BFU-E) were enumerated. Similar colony growth was achieved in all media for PB; modestly increased BM CFU-GM were noted in SCCK. SCCK and RM are easy to use, are commercially available with lot-controlled conditioned media (PHA-LCM), and may facilitate the standardization of CFU assays in blood banks and bone marrow processing laboratories.