Blood vessel formation includes vasculogenesis and angiogenesis. Traditionally vasculogenesis is believed to occur in embryo, forming blood vessels by the differentiation of angioblasts, while angiogenesis is defined as the formation of new blood vessels that originate from pre-existing vessels, which happens both in embryo and adult. However, recent studies on angioblasts have shown that new blood vessel formation due to angioblast differentiation, once was believed to happen exclusively in embryo, also occurs in adult. These findings not only help us to understand the pathogenesis of new blood vessel formation, but also provide some new clues to investigate new therapeutic target for the treatment of angiogenesis. Eye Science 2005 ;21:158-162. Blood vessel formation includes vasculogenesis and angiogenesis. Traditionally vasculogenesis is believed to occur in embryo, forming blood vessels by the differentiation of angioblasts, while angiogenesis is defined as the formation of new blood vessels that originate from pre-existing vessels, which happens both in embryo However, and adult. However, recent studies on angioblasts have shown that new blood vessel formation due to angioblast differentiation, once was believed to happen exclusively in embryo, also occurs in adult. These findings not only help us to understand the pathogenesis of new blood vessel formation , but also provide some new clues to investigate new therapeutic targets for the treatment of angiogenesis. Eye Science 2005; 21: 158-162.