Reactive oxygen species (ROS) are believed to be important molecules in the regulation of angiogenesis. However, direct evidence is obtained from hydrogen peroxide only. The comparison of superoxide anion (O2-), hydrogen peroxide (H202) and hydroxyl radical (HO*) effects on angiogenesis in one angiogenic model were studied. Tube formation, migration and adhesion of endothelial cells were enhanced with a low concentration of O2 generated by 500 [microM xanthine (X) and 1 mU/ml xanthine oxidase (XO), but significantly inhibited as the XO increased to 10 mU/ml or more. Low concentrations of H2O2 (0.01-1 microM) induced tube formation and the maximal tube formation was achieved at 0.1 microM which also induced cell migration and adhesion, while high concentrations of H2O2 (100 microM) inhibited tube formation and cell migration. Both H2O2 and O2 inhibited cell proliferation at high concentration only. HO* at low concentration neither inhibited nor stimulated the tube formation, cell proliferation and migration but inhibited at high concentration. The effects of O2 were significantly abolished by catalase (CAT) alone or in combination with superoxide dismutase (SOD), but not by inactive CAT or SOD alone. Active CAT, but not inactive CAT, also reversed the effects of H2O2. Pretreatment with GSH effectively reversed the inhibitory effects of HO*. Therefore, our results suggest that ROS have biphasic effects on angiogenesis, which indicated that pharmacologically regulating cellular ROS levels might serve as an anti-angiogenic or angiogenic principles. They also provide a theoretical basis for the development and rational use of novel angiogenic and anti-angiogenic drugs.