Antimitotic agents comprising a modified chalcone or modified chalcone derivative are disclosed. The modified chalcone or modified chalcone derivative compounds are of the general formula CHAL-LIN--COV, wherein CHAL is a chalcone or chalcone derivative portion, LIN is an optional linker portion, and COV is a covalent bonding portion (e.g., an .alpha.,.beta.-unsaturated thiol ester group). The modified chalcone or modified chalcone derivative compounds provide an improved method of interference with tubulin polymerization, for example by covalent (and essentially irreversible) bonding between tubulin and the covalent bonding portion, potentially resulting in a decrease in tumor size and/or disappearance of the cancer, to the benefit of cancer patients.