Plant senescence is a natural regulated and programmed process that leads ultimately to cell death. As soon as it emerges, Zantedeschia aethiopica spathe undergoes senescence, displaying the common features of this process in leaves, such as protein and chlorophyll losses and decline in photosynthetic ability. When pollination occurs, the spathe senescence is naturally inhibited and its regreening takes place. In this work, APX (ascorbate peroxidase) and cytCu/Zn-SOD (superoxide dismutase) activities and expression analysis were evaluated during Z. aethiopica spathe development. The high expression of cytCuZn-Sod during the initial stages of spathe whitening, together with a strong repression of Apx expression in the same stages, suggests the hypothesis of an initial H2O2 burst leading to the senescence progression. The content in hydrogen peroxide during the time course of Z. aethiopica spathe development was determined. The results show a significant increase in the levels of H2O2 during the initial stages of the whitening process, which could be mainly due to the differential expression of Apx and cytCuZn-Sod genes in those stages. The increase in H2O2 level continues until the white spathe but in this case the main source is probably the senescence process itself. Lipid peroxidation that measures the level of oxidative damage follows the same pattern as H2O2 levels suggesting a cause/effect relationship.