Four synthetic curcuminoids, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3, 5-dione (curcumin1), 1,7-bis(piperonyl)-1,6-heptadiene-3, 5-dione (piperonyl curcumin), 1, 7-bis(2-hydroxy naphthyl)-1, 6-heptadiene-2, 5-dione (2-hydroxy naphthyl curcumin), 1,1-bis(phenyl)-1, 3, 8, 10- undecatetraene-5, 7-dione (cinnamyl curcumin) and their copper(II) complexes were investigated for their possible cytotoxic and antitumour activities. Copper chelates of synthetic curcuminoids showed enhanced antitumour activity. All the compounds were found to be cytotoxic to cultured L929 cells, concentration needed for 50% inhibition being around 10 microg/ml for curcuminoids and 1 microg/ml for their copper complexes. Copper complexes of curcuminoids with a hydroxy group on the ring such as 2-hydroxy naphthyl curcumin were found to be most active (1 microg/ml produced 60.45+/-2.1% cell death). Copper complex of cinnamyl curcumin which has an extended conjugation showed considerable activity in increasing the life span (ILS=78.6%) of ascites tumour bearing animals. Whereas complex of piperonyl curcumin was found to show least antitumour activity. Copper chelates of curcuminoids showed a significant reduction (p< .001) of solid tumour volume in mice.