The reaction between (aminoimino)methanesulfinic acid, HO2SC(NH)NH2 (AIMSA), and bromate has been studied in acidic medium. In excess AIMSA the stoichiometry of the reaction is 2BrO(3)- + 3AIMSA + 3H(2)O --> SO42- + 3CO(NH2)2 + 2Br(-) + 6H(+), and in excess bromate the stoichiometry is 4BrO(3)- + 5AIMSA + 3H(2)O --> 5SO(4)(2-) + 5CO(NH2)(2) + 2Br(2) + 6H(+). Br-2 is produced only when BrO3- is in stoichiometric excess over AIMSA. It is produced from the reaction of the product, Br-, with excess BrO3- after all the AIMSA has been consumed. The reaction has an initial induction period followed by formation of bromine. Although AIMSA is oxidized to SO42-, no SO42- formation is observed until Brz production commences. The reaction is autocatalyzed by bromide. The reactive oxidizing species in solution are HOBr and Br-2. Bromide enhances their formation from bromate. A simple eight-reaction mechanism is used to describe the reaction. The reaction commences through a direct reaction between BrO3- and AIMSA : BrO3- + HO2SC(NH)NH2 + H+ --> HBrO2 + HO3SC(NH)NH2 with k = 2.5 x 10(-2) M(-2) s(-1). The rate-determining step is the standard BrO3- Br- reaction which forms the reactive species HOBr : BrO3- + Br- + 2H(+) --> HBrO2 + HOBr. A computer simulation analysis of the proposed mechanism gave good fit to the data.