The chlorate-bromide reaction, ClO3- + 6Br(-) + 6H(+) -> 3Br(2) + Cl- + 3H(2)O, was followed at the Br-3(-)/Br-2 isosbestic point (446 nm). A fifth-order rate law was found: (1)/(3) d[Br-2]/dt = k[ClO3-][Br-][H+](3) (k = 5.10 x 10(-6) s(-1) L-4 mol(-4)) at 25 degrees C and I = 2.4 mol L-1. At high bromide concentrations, the bromide order becomes close to zero, indicating a saturation profile on bromide concentration, similar to the chloride saturation profile observed in the chlorate-chloride reaction. A mechanism is proposed that considers the formation of the intermediate BrOClO22-, similar to the intermediate ClOClO22- proposed in the mechanism of the chlorate-chloride reaction.