Abstract: Response of the Allium cepa genetic material to the presense of potential cytotoxic and genotoxic substances in aquatic environment was used to evaluate the toxicity of industrial wastewater collected from 4 different sites: Shawa, Meet El Akrad, Telbana and Belgay along the new Mansoura drain in Sandub area, Dakahlia Province. For in situ monitoring of the cytotoxicity level, the inhibition of mitotic division in meristematic cells, was assayed. For testing the genotoxicity of the collected water samples, two assays were used, chromosome aberration assay in mitotic cells and micronucleus assay (MNC) in interphase cells. The results indicate that all the water samples collected from the drain were highly mutagenic. Concentrations of the heavy metals (Pb, Zn, Co, Cd, Cu) were also determined and could partly be correlated with the toxicity of water and industrial load of Sandub area.