In vitro cell-based assays were developed, optimized and validated to assess the cytotoxicity of colchicine, and the ability of specific ovine polyclonal antibodies and their Fab fragments to neutralize and, possibly, reverse these cytotoxic effects. The assays were based on measuring the effects of colchicine on Vero cells in a monolayer culture, as assessed by the visual appearance of cell rounding, and by a loss of elec. impedance as determined by real-time electronic sensing. Colchicine did not impair the ability of Vero cells to take up neutral red. The cytotoxicity of colchicine was time and dose-dependent. Maximum cell rounding of up to 90% of Vero cells occurred after 16-24 h at a concentration of 1000 μg/L. The lethal cytotoxic dose (LC50) that results in 50% cell rounding was 220 μg/L. Equimolar amounts of polyclonal anti-colchicine Igs and a Fab-based immunotherapeutic product, ColchiBind, completely inhibited the cytotoxic effects of colchicine when added simultaneously or up to 2 h after the addition of colchicine to the Vero cultures. Considerable protection was also provided when the addition of antibodies or ColchiBind was delayed for 4 h, but a further delay was associated with progressive, irreversible effects and by 8 h the protective effect was negligible.