This paper presents a study on the reactivity of natural limestones from five deposits in Turkey. The conversion rates of carbonates in size fractions of the samples were measured in a stirred suspension of 2.5 1 at 20 degreesC and a constant-pH value of 5 obtained with the addition of HCl solutions by a pH control pump. Particle size and the dolomite content of the limestones were found to be the most influential parameters in the reactivity measurements. (C) 2003 Elsevier Ltd. All rights reserved.