MORAb-004 is a monoclonal antibody directed against endosialin, a cell surface glycoprotein, which is expressed on cells involved in tumor vasculature. Studies have found endosialin to play a key role in tumor growth and neovessel formation in numerous cancer types including melanoma. Preclinical pharmacological studies have shown that MORAb-004 is a potentially useful anti-cancer agent. This clinical trial is being performed to determine the efficacy of MORAb-004 at two dose levels in subjects with metastatic melanoma, as well as to establish serum pharmacokinetics and pharmacodynamics of the antibody.