Data obtained on the distribution of strontium in limestones and dolostones of the Middle Limestone Group (Carboniferous) in England show that most of the strontium in the limestones (Sr = 618 + or - 267 ppm, mSr (super 2+) /mCa (super 2+) = 0.7 X 10 (super -3) ) was removed by dolomitization and only a small fraction was retained within the newly formed dolostones (Sr = 132 + or - 46 ppm, mSr (super 2+) /mCa (super 2+) = 0.225 X 10 (super -3) ). The strontium of the resulting dolostone appears to be located in the dolomite lattice. Little of it could be related to the insoluble residue of these rocks, suggesting that none or little of the strontium liberated during dolomitization was adsorbed onto clay minerals. Data obtained on the strontium distribution in some associated recently dedolomitized dolostones show that the strontium content of dolostones suffered a considerable loss during dedolomitization (Sr = 95 + or - 26 ppm, mSr (super 2+) /mCa (super 2+) = 0.157 X 10 (super -3) ). However, in view of the fact that the dedolomitization of the dolostones was affected by modern seawater and not by meteoric water (Al-Hashimi and Hemingway, 1973), this loss should not have taken place: the strontium content and the mSr (super 2+) /mCa (super 2+) ratio of the dedolomites would be expected to be similar to the strontium content and to the mSr (super 2+) /mCa (super 2+) ratio of a calcite precipitated from seawater in equilibrium with the atmosphere, i.e., Sr = 1,110 ppm, mSr (super 2+) /mCa (super 2+) = 1.26 X 10 (super -3) . The present strontium content and mSr (super 2+) /mCa (super 2+) ratio of the dedolomitized rocks suggests that the mSr (super 2+) /mCa (super 2+) ratio of the dedolomitizing solution, i.e., seawater, must have suffered a considerable dilution while dedolomitizing the dolostones. This dilution could be achieved only through the dissolution of altered dolomite crystals.