Identified are the natural isotopes of five possible structural materials or alloying constituents (Mo, Ni, Cr, Fe, V) which theoretically produce the lowest level of induced radioactivity, biological hazard potential (BHP), and afterheat in a fusion reactor. Activity is examined at shutdown and at very long times after blanket disposal (1000 years). The analyses have been carried out using blankets designed for the WITAMIR-I D-T and the SATYR D-D fueled tandem mirror reactors.