UV-vis stopped-flow studies of the reaction of [Ru(NH3)(5)isn](2+) (isn = isonicotinamide) with excess HOCl at 25 degreesC demonstrate that it proceeds in two time-resolved steps. In the first step [Ru(NH3)(5)isn](3+) is produced with the rate law -d[Ru(II)]/dt = 2(aK(h)[H+] + b[H+][Cl-] + c[Cl-])[HOCl](tot)[Ru(II)]/(K-h + [H+][Cl-]). Here, K-h is 1.3 x 10(-3) M-2 and corresponds to the equilibrium hydrolysis Of Cl-2, a is (8.34 +/- 0.19) x 10(3) M-2 s(-1) and represents the acid-assisted reduction of HOCl, b is (4.04 +/- 0.13) x 10(4) M-1 s(-1) and represents the reduction of Cl-2, and c is (6.25 +/- 0.59) x 10(2) s(-1) and represents the Cl-assisted reduction of HOCl. In the second step [Ru(NH3)(5)isn](3+) undergoes further oxidation to a mixture of products with the rate law -d[Ru(III)]/dt = e[Ru(III)][HOCl]/ [H+] where e is (1.18 +/- 0.01) x 10(-2) s(-1). This step is assigned a mechanism with Cl- transfer from HOCl to [Ru-III(NH3)(4)(NH2)isn](2+) occurring in the rate-limiting step. These results underline the resistance of HOCl to act as a simple outer-sphere one-electron oxidant.