Genotoxic effects of Dursban 4 (Chlorpyrifos-Ethyl), which is used commonly in agricultural areas were evaluated in the root meristem cells of Allium cepa. The roots of the plants were treated with 600 ppm, 1200 ppm and 1800 ppm concentrations of Dursban 4. Root tips after having grown to a certain length were stained according to aceto-orcein squash procedure. Metabolic variations in response to Dursban 4 toxicity was measured using physiological parameters and antioxidant enzymatic activities. Chromosomal aberrations, mitosis abnormalities, mitotic index and micronucleus assay of applied pesticides on Allium cepa roots were determined.