To identify novel inhibitors of the STAT5 signaling pathway, these ten natural and synthetic chalcones as well as curcumin were tested for their ability to suppress IL-3-mediated induction of the STAT5 target gene Cis. The gene Cis was selected for the initial screen as it is a well characterized STAT5-dependent gene [3], [46], [47], [66] and a potential therapeutic target in STAT5-associated cancers [67]. The gene discussed is STAT5A; the disease is cancer.