Hydrogen peroxide is a molecule natively generated in plants during the normal physiological processes. However, under stress conditions it can be massively produced and can become toxic for the cells. Recently other authors reported that the exogenous application of hydrogen peroxide in low concentrations renders protection of plants against different stress factors. In this investigation we report the protective role of preliminary treatment with H2O2 against the toxic action of the herbicide paraquat in pea plants. The changes in some physiological parameters, such as plant survival, content of malondialdehyde, leaf pigments and photosynthetic rate were determined in relation to the paraquat toxicity in H2O2-treated plants.