Rate coefficients for the reaction between HO2 and ClO radicals were obtained using the discharge-flow/mass-spectrometry technique at total pressures of 1.1-1.7 Torr of He, and between 298 and 215 K. The room-temperature rate constant, determined using seven different combinations of HO2 and ClO precursors, was found to be (7.1 +/- 1.8) x 10(-12)(+/-2 sigma) cm(3) s(-1). The temperature-dependent overall reaction rate coefficient is described by k((3)) (298-215 K) = (7.1 +/- 0.4) x 10(-12) exp(-16 +/- 17/T) cm(3) s(-1). The previous observation of a strong negative temperature dependence in the title reaction below 298 K was not observed, resulting in a significantly lower rate coefficient at stratospheric temperatures. HOCl was the only product of the reaction, and an upper limit of 1% for the branching ratio for the formation of O-3 and HCl was obtained at the low pressures of these experiments.