Preliminary trials have illustrated that monoclonal antibodies can be administered safely, tumor binding can be achieved, and sensitive radioimaging may be possible. Additionally, clinical responses in patients with colorectal carcinoma can occur. The limitations of murine monoclonal therapy are now being addressed and in time will be overcome. Monoclonal antibodies offer great promise in the diagnosis and therapy of malignant disease. Further investigation using innovative approaches and in combination with other therapies may help to reach this goal.