In vitro studies showed that several flavonoids, tannic acid, gallic acid and fat-soluble vitamins inhibited HeLa and Raji lymphoma cell growth. The inhibition trend exhibited by these compounds was similar for both cell lines, and their growth was inhibited dose dependently. Butein, (10 microM), the most potent anti-proliferative agent, exerted 30% growth inhibition and was more effective on HeLa cells. Retinol (100 microM) inhibited cell proliferation completely. Tannic acid was twice as potent as its monomer gallic acid. From structure-activity consideration, the C2,3-double bond of the flavonoid molecule was important for activity. Flavonoid aglycones were more effective than their corresponding glycosides in suppressing cell growth.