The pyrolysis of BH3. SMe2 at 130 degrees C and 1000 psi yields isomers of (Me2S)(2)B12H10. The previously unreported 1,2 isomer has been isolated and characterized by single-crystal X-ray analysis and multinuclear NMR spectroscopy. Its physical and spectral characteristics are compared to those of the earlier reported 1,7 and 1,12 isomers of (Me2S)(2)B12H10.