Genetic improvement in maize (Zea mays L.) is associated with increased stress tolerance, but the physiological mechanisms that confer general stress tolerance have not been identified. Darwin suggested that hybrid vigour conferred stress tolerance and maize hybrids and their parental inbred lines could function as a model for the identification of physiological mechanisms. This study was undertaken in an outdoor hydroponic system at Guelph, Ontario in 2004 to show how the hybrids are more tolerant to environmental stresses than their parental inbred lines, and if there is a common physiological mechanism associated with stress tolerance to each of the stresses, including light, water, and nitrogen. Genetic materials were the maize hybrid CG60xMBS1236 and its parental inbred lines. The stress treatments include light stress (55% light reduction by artificial shading vs. control), water stress (50% water supply relative to the control), and nitrogen stress (no nitrogen supply during treatment periods). The stresses were imposed for a 3-week period during two developmental phases (from 1 week pre-silking to 2 week post-silking, i.e stress I, and from 2 to 5 week post-silking, i.e. stress II). The overall results suggested that grain yield and dry matter reduction occurred at both stress periods but the reductions were much greater in the stress I than stress II. The hybrid was more tolerant to stresses, especially the light stress. For the first period of light stress, the yield reduction was 4.6 times higher for the mean of two inbred lines (54.6%) compared to the hybrid (11.8%). The yield decrease under stresses was associated with reduced rate of leaf photosynthesis, increased rate of leaf senescence, and most importantly the kernel establishment capability of the genotype.