A series of 4-carboxychalcones 1 were prepared and coupled to 3,5-bis(phenylmethylene)-4-piperidone (2) giving rise to a novel series of N-[4-(3-aryl-3-oxo-1-propenyl)phenylcarbonyl]-3,5-bis(phenylmethylene)-4-piperidones (3). Molecular simplification of the amides 3 led to the formation of the corresponding N-(3-aryl-1-oxo-2-propenyl)-3,5-bis(phenylmethylene)-4-piperidones (4). A cytotoxic evaluation of the compounds in series 1-4 utilized murine P388 and L1210 cells as well as human Molt 4/C8 and CEM T-lymphocytes. In general, the compounds displayed significant toxicity; the IC(50) values of 54% of the enones were less than 10 microM when all four screens were considered and less than 1 microM for all members of series 3 in the P388 assay. Various correlations were established between the potencies of the compounds in series 1, 3 and 4 and the Hammett sigma, Hansch pi and molecular refractivity constants of the aryl substituents. Several torsion angles and interatomic distances of five representative compounds in series 3 and 4 were determined by X-ray crystallography, some of which contributed to the observed bioactivity. The marked cytotoxicity and lack of murine toxicity of most of the compounds described in this study, as well as their selective toxicity towards different tumour cell lines, revealed that development of the enones 2-4 as novel candidate antineoplastic agents should be pursued.