Reactive uptake coefficients for HOCl as a function of [HCl] were measured in a rotating wetted-wall flow reactor for several sulfuric acid solutions containing between 49 and 67 wt % H2SO4 at 220 and 250 K. The solubility of HOCl in sulfuric acid solutions at 220 and 250 K was also measured. Using these measured solubilities, calculated HCl solubilities, and estimated diffusivities for HOCl, the second-order rate coefficients (k(II)) in the liquid were extracted. At 250 K, k(II) increases with increasing acid concentration, from 3 x 10(5) M-1 s(-1) at 49 wt % acid to 5 x 10(6) M-1 s(-1) at 67 wt %. It is suggested that the reaction may involve an initial protonation of HOCl, followed by reaction of H2OCl+ with Cl-.