There is circumstantial evidence implicating reactive oxygen species (ROS) in the highly ordered temporal and spatial regulation of expression of the Cat and Sod antioxidant genes during seed development and germination in maize. In order to understand and provide experimental data for the regulatory role of ROS, the expression patterns of the Cat1, Cat2, Cat3, GstI, Sod3, Sod4, and Sod4A genes, as well as catalase (CAT) and superoxide dismutase (SOD) activity responses, were examined after treatments with ROS-generating xenobiotics in developing and germinated maize scutella. CAT and SOD activities increased at both stages in response to each xenobiotic examined in a dose-dependent and stage-specific manner. Individual Cat gene expression patterns were co-ordinated with isozyme patterns of enzymatic activity in scutella of developing seeds. This was not observed in germinated seeds where, although Cat1 expression was highly induced by ROS, there was not a similar increase of enzymatic CAT1 activity, suggesting the involvement of post-transcriptional regulation. Enhanced enzyme activities were synchronous with increases in steady-state transcript levels of specific Sod genes. The steady-state transcript level of GstI was elevated in all samples examined. Gene expression responses derived from this study along with similar results documented in previous reports were subjected to cluster analysis, revealing that ROS-generating compounds provoke similar effects in the expression patterns of the tested antioxidant genes. This could be attributable to common stress-related motifs present in the promoters of these genes.