Evidence is given for a stepwise mechanism in the Dushman reaction by using accelerated-flow mixing to measure reaction rates at high [H+] and [I-], where pseudo-first-order rate constants vary from 213 to 6700 s(-1). The typical [H+](2) dependence is lowered due to the formation of appreciable [HIO3]. The typical [I-](2) dependence is lowered because I2O2 is a steady-state intermediate, The rate expression is: -d[IO3](T)/dt = k(1)(k(2)/k(-1))K-H[H+](2)[I-](2)[IO3](T)/[(1 + K-H[H+])(1 + (k(2)/ k(-1))[I-])], where k(1) = 4.8 x 10(7) M-2 s(-1), k(2)/k(-1) = 2.3 M-1, and K-H = 2.5 M-1 at mu = 0.50 M, 25 degrees C.