The synthesis of tert-butylarsine-d2 from tert-butylarsenic dichloride and LiAlD4 is described. No resonances at 2.65 ppm (from AsH2) are observed in the 1H NMR spectrum, indicating the isotopic purity is greater than 95%. The pyrolyses of tert-butylarsine and tert-butylarsine-d2 were studied by using a flow reactor operated between 425 and 550 °C at total pressures of 0.001, 5, and 700 Torr. At 5 and 700 Torr, nitrogen was used as the carrier gas. The volatile products of the reaction were trapped in a liquid nitrogen cooled trap, transferred under vacuum into an NMR tube, and quantitatively analyzed by using 1H NMR spectroscopy. Three important results from the study are (1) the isobutane produced during the pyrolysis of tert-butylarsine-d2 was Me3CD, (2) C2Me6 was proven not to be a product of the reaction, (3) isobutane was found to be the major product at atmospheric pressure, while isobutene was predominant at low pressures in agreement with previous studies. These data allow us to evaluate the possible mechanisms for the pyrolysis and discard a mechanism involving radical non-chain reactions.