A radioimmunoconjugate consisting of 81C6, a murine IgG2 anti-tenascin monoclonal antibody labeled with iodine 131 (I-131), with radioimaging and radioimmunotherapeutic activities. Using monoclonal antibody 81C6 as a carrier for I-131 results in the targeted imaging and/or destruction of cells expressing tenascin. Tenascin is an extracellular matrix protein which is overexpressed in gliomas and other cancers.