Theaflavins, flavonoids found in black tea, exhibit a variety of health-promoting activities, but the mechanisms by which they act are not clear. Here, we assess the effects of black tea extract and isolated theaflavins on Dictyostelium discoideum, a model organism exhibiting an unusual life cycle relying on conserved pathways involved in human disease. Dictyostelium has been used to characterize the activities of numerous bioactive small molecules, including catechins, from which theaflavins are produced during the preparation of black tea. We show that theaflavins block growth, development, and motility in Dictyostelium, results that suggest catechins and theaflavins exert similar activities in this organism. (C) 2017 Elsevier Inc. All rights reserved.