Apigeninidin, a 3-deoxyanthocyanidin present in sorghum, was chemically synthesized and effectively purified by extracting impurities from aqueous 2 N HC1 into ethyl acetate. Apigeninidin (50μmol) applied to filter paper disks inhibited the growth on agar plates of selected gram-positive bacteria (Bacillus cereus, Staphylococcus aureus, Staphylococcus epidermidis, andStreptococcus faecalis) and to a lesser extent gram-negative bacteria (Escherichia coli, Serratia marcens, andShigella flexneri). Apigeninidin was not mutagenic based on the Ames assay. The ability of apigeninidin to precipitate proteins from plant extracts could be physiologically important if it can be shown to bind to specific plant proteins.