The effects of high light (1500 mumol m(-2) s(-1)) on photosynthetic characteristics and antioxidant enzyme capacity of the monocotyledonous resurrection plant Xerophyta viscosa Baker and the crab grass Digitaria sanguinalis L. were investigated as a function of time for 20 days of treatment. High light treatment caused photoinhibition in D. sanguinalis, whereas X. viscosa was less affected. The reduction in photochemical efficiency of PSII in X. viscosa during high light probably contributed to the decline in the photosynthesis rate, since other factors such as intercellular CO2 concentration, chlorophyll a + b, and carotenoid content were not markedly changed. On the other hand, the net photosynthesis rate of D. sanguinalis declined considerably during the high light treatment, probably, in part, due to the decline in photochemical efficiency of PSII. The increase in the transpiration rate corresponded to an increase in stomatal conductance in both species. Long-term high light brought about photosynthetic pigment chlorophyll (a + b) loss and membrane leakage in D. sanguinalis only. While concentration of anthocyanin increased in both species, carotenoid increased only in D. sanguinalis. High light caused significant activation of all superoxide dismutase (SOD) isoenzymes, especially Cu/ZnSOD, in both species. However, total SOD activity of X. viscosa was significantly greater than D. sanguinalis during the high light treatment. The total peroxidase and glutathione reductase activity and isoenzyme amounts of D. sanguinalis were significantly higher than those of X. viscosa, and levels increased in the former only during high light treatment.