The characteristic pattern of differential cytotoxicity of a crude extract of the tropical plant Potymtifruticosa was found to be similar to those of known tubulin-interactive compounds. Fractionation of the extract led to centaureidin as the major cytotoxic principle. Centaureidin inhibited tubulin polymerization, inhibited the binding of [3H]-colchicine to tubulin, and induced mitotic figure formation in whole cells at cytotoxic concentrations. This is the first known example of a flavone with antimitotic activity.