The human colon adenocarcinoma-derived cell line CaCo-2 male Swiss mice and male Sprague-Dawley rats were used as model systems to study the effects of nickel (II), 5-methyl-2-furaldehyde thiosemicarbazone ligand and their complex. The stimulation effect of the complex was obtained with low concentrations from 3.7 x 10(-7) to 3.7 x 10(-6) M, while inhibiting effects occurred from 3.7 x 10(-5) to 3.7 x 10(-4) M. This study showed that Ni (II) is toxic for cultured cells. Our data suggest that the comple; according to the toxicity assays in mice and carcinogenesis assays in rats, could be used as an antimitotic agent.