The paper describes the effect of limestone type and grind on SO2 scrubber performance. It gives results of a comparison of the amount of limestone feed required as a function of particle size, to obtain a given SO2 removal efficiency and, thus, to verify the relative magnitude of the effect of limestone grind observed during an earlier study. Experimental data were also obtained with limestones from four different quarries ground to similar sizes to test the geological or type effect on limestone reactivities. It also gives results of a test of the effectiveness of wet screen analysis as a means of classifying limestone grinds for scrubber use. A mass-transfer model and Coulter-counter particle-size distribution data were also tested as a means of defining limestone reactivities. The cost-reduction effect of finer limestone grinding on SO2 scrubber efficiency was found to be considerable.