Most chronic (long-lasting) wounds of the leg (also known as venous ulcers) fail to heal in a reasonable period of time. Although researchers have made great progress in understanding how the body repairs wounds, attempts to develop new treatments have been disappointing. In general, treatments based on recent findings about the details of wound repair have not greatly reduced the number of people who have chronic wounds. The long-term goal of this study is to evaluate a new approach for healing a chronic wound. Current methods of directly applying substances that are involved in wound healing to a chronic wound do not cause enough healing. PDGF-B (platelet-derived growth factor B), a factor associated with wound healing, might dramatically enhance healing if a genetically engineered virus is injected into the wound that causes cells in the wound to produce PDGF-B in large quantities.