Dibenzoylmethane (DBM), a minor beta-diketone constituent of licorice and sunscreens, has been shown to exhibit anti-neoplastic effects in chemically induced skin and mammary cancers in several animal models. To date, no mechanism for the growth inhibitory effects of DBM on prostate cancer cells has been proposed. In this study, we examined the effects of DBM on the growth and cell cycle kinetics of several human prostate carcinoma cell lines. Using an MTT cytotoxicity assay, IC50 values of 25-100 microM were observed following 72 h exposure to DBM. LNCaP, DU145, and PC-3 prostate carcinoma cell lines were particularly sensitive in comparison to the cells with the vehicle alone. Flow cytometric analyses showed deregulation of the cell cycle, which correlated with the observed cytostatic effects of DBM in prostate carcinoma cells. These data suggest a potential role for DBM in the prevention and treatment of prostate cancer.