The kinetics and the mechanism of the reaction BrO + CH3SH --> P (1) have been studied using the mass spectrometric discharge-flow method over the temperature range 259-333 K and at low total pressure between 0.5 and 3 Torr. The temperature dependence of the reaction rate constant has been determined under pseudo-first-order kinetic conditions in excess of CH3SH over BrO radicals. k = (2.2 +/- 1.9) x 10(-15) exp[(827 +/- 255)/T] cm(3) molecule(-1) s(-1). The reaction has been found to be pressure dependent in the pressure range studied. The experimental evidences suggest an addition mechanism. The studied reaction constitutes an efficient atmospheric sink for the reduced sulfur compound. CH3SH. (C) 2002 Published by Elsevier Science B.V.