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Genotoxicity of peracetic acid (PAA) has been assessed in two models (protocols) of Allium cepa conducting two sets of experiments to know whether the results would be model dependent. One experiment was set as per Fiskesjo's model in which Allium cepa bulbs were grown in five concentrations of peracetic acid (0.039, 0.078, 0.156, 0.312 and 0.625 ppm) in tap water. Another experiment was set as per Rank and Nielson's model in which Allium cepa bulbs were first grown in tap water for 24 hours and were then further grown in the same concentrations of peracetic acid as in earlier model. Genotoxic effects of peracetic acid were assessed in both models using usual parameters i.e. shape, colour and length of root tips, mitotic index, chromosomal aberrations and cell death. Magnitude of effect differed significantly in both models. More severe genotoxic effects could be seen in Fiskesjo's model. It is suggested that root primordial cells were in G0 state in Fiskesjo's model, which presumably lacked their defense system, hence were more prone to peracetic acid toxicity. Mitotically dividing root cells in Rank and Nielsen's model were equipped with antioxidant system and were more resistant to peracetic acid