Abstract Time-resolved polarograms of the intermediate generated successively in the reduction of BrO − 3 (i.e. BrO 2 . radical and bromite ion) have been measured by the method of laser photoelectron emission from a metal into a solution. For E > −0.83 V (vs. SCE) in alkali solutions, bromite ion is electrochemically stable on a mercury electrode, and the reduction of BrO 2 . is due to homogeneous bimolecular generation of BrO . radical in the reaction of BrO 2 . with BrO − 2 ( K - 10 9 M −1 s −1) and its subsequent three-electron reduction to Br −, so that the stoichiometric number ν (the ratio of the number of electrons transported into a solution to the number of those trapped by BrO − 3 ion) is equal to 3. For E < −1.1 V, when the reduction rate constant for BrO 2 − becomes larger than 0.2 cm s , successive five-electron reduction of BrO 2 . radical is observed and v = 6. The transfer coefficient for BrO − 2 reduction equals 0.40 ± 0.05. The decrease of ν for E > −1.0 V does not occur when NH 4 + ions are introduced into the solution in a concentration exceeding 7 × 10 −2 M, and it gives rise also to an increase of the BrO 2 − reduction rate by some orders of magnitude. A mechanism of the electrode reduction of BrO 3 − ions is proposed in which the overvoltage is caused by the formation of energy-enriched intermediates in the first one-electron stage with the participation of proton donors.