The deuterium-labeled 6,9-[(CH3)(2)S](2)-2,4-D2B10H10 is formed regiospecifically from 2,4-D2B10H12 and (CH3)(2)S. Likewise, the deuterium labels are retained in the same relative locations when 6,9-[(CH3)(2)S](2)-2,4-D2B10H10 is converted to 5-[(CH3)2S]-2,4-D2B10H10, by thermal ligand displacement, and to 5-[(CH3)(2)S]-9-(Thx)-2,4-D2B10H9 by hydroboration of 2,3-dimethyl-2-butene.