To examine the influence of HCl on SO2 removal in the spray dry scrubbing process, preliminary experiments on the effect of adding CaCl2 to the lime slurry On SO2 absorption efficiency were performed in a laboratory scale spray dryer. It was found that the SO2 removal efficiency is augmented at CaCl2 concentrations up to 1.2 g/l in the lime slurry. This is ascribed to the influence of the prolonged drying process. However, SO2 absorption efficiency cannot be improved further at higher CaCl2 concentrations. A simple estimation shows that this cannot be ascribed solely to the influence of the drying behavior of the droplets and more complex explanations have to be found. Subsequently, experiments on the simultaneous absorption of SO2 and HCl were performed. It was found that the SO2 removal efficiency is enhanced at low HCl concentrations in the flue gas. This is ascribed to the formation of CaCl2 in the droplets, resulting in a prolonged drying process. After reaching a maximum, the SO2 removal efficiency falls again at higher HCl concentrations. This can be explained with the competing absorption process in which HCl is thermodynamic ally favored.