A solution of B,B',B ''-tribromoborazine (BrBNH)(3) in excess C6D6 in a sealed NMR tube shows no changes for over 14 months at room temperature but undergoes fast (within minutes) HID exchange in the presence of AlBr3 as a Lewis acid, as evidenced by H-1, H-2, B-11, and Al-27 NMR spectroscopy. The proposed electrophilic exchange mechanism is in agreement with the results of DFT computations. To our knowledge, this is the first example of the electrophilic substitution reaction of borazines in solution.