Angiogenesis is a major factor in the development of benign, inflammatory, and malignant processes of the skin. Endothelial cells are the effector cells of angiogenesis, and understanding their response to growth factors and inhibitors is critical to understanding the pathogenesis and treatment of skin disease. Hemangiomas, benign tumors of endothelial cells, represent the most common tumor of childhood. In our previous studies, we have found that tumor vasculature in human solid tumors expresses similarities in signaling to that of hemangiomas, making the knowledge of signaling in hemangiomas widely applicable. These similarities include expression of reactive oxygen, NFkB and akt in tumor vasculature. Furthermore, we have studied malignant vascular tumors, including hemangioendothelioma and angiosarcoma and have shown distinct signaling abnormalities in these tumors. The incidence of these tumors is expected to rise due to environmental insults, such as radiation and lumpectomy for breast cancer, dietary and industrial carcinogens (hepatic angiosarcoma), and chronic ultraviolet exposure and potential Agent Orange exposure. I hypothesize that hemangiomas, angiosarcomas, and vascular malformations represent the extremes of signaling abnormalities seen in pathogenic angiogenesis.