Fifteen curcumin analogs were synthesized and tested for in-vitro cytotoxicity towards B16 and L1210 murine cancer cell lines using an MTT assay. Significant activity was discovered for two analogs: 8 (B16 IC(50) = 1.6 microM; L1210 IC(50) = 0.35 microM) and 9 (B16 IC(50) = 0.51 microM; L1210 IC(50 )= 1.2 microM). Several other analogs exhibited notable cytotoxicity. The data from quantitative structure-activity relationships suggest that large electron-withdrawing substituents placed in the meta-position of the arylidene aryl rings enhance potencies. Compounds 8 and 9 were found using a cell-based assay to have virtually no effects on microtubules at concentrations up to 40 microM. These results suggest that tubulin inhibition is not the principal mechanism by which the curcumin analogs act.