A highly effective and operationally practical method for the regioselectivedeuteration of N-alkyl-substituted anilines employing Ru3(CO)12 (⩽1 mol %) as catalyst and D2O as deuterium source was described. A variety of N-alkyl-substituted anilines were efficiently deuterated (up to 98%) at the ortho and/or para position with respect to the nitrogen at neutral conditions. Under the present conditions