Abstract Time series experiments relating to the dolomitization of calcite at 215° to 225°C in saline solutions of near-seawater salinity were conducted to ascertain the influence of sulfate and carbonate in solution on the rate of calcite dolomitization. A concentration of about 0.004M sulfate in solution prevented the dolomitization of calcite. At concentrations of less than 0.004M, dolomitization proceeded at a slower rate than in experiments where no sulfate was present. The final concentration of sulfate was controlled by the precipitation of anhydrite. The presence of sulfate in solution did not prevent the direct precipitation of dolomite in experiments in which the solid reactants were carbonate minerals other than calcite (BaCO 3 and 2PbCO 3 .PbOH). Also, the presence of sulfate in the calcite dolomitization experiments slowed the rate of calcite dissolution from 3 days in sulfate-free solutions to 6 or 7 days in sulfate-bearing solutions. These observations indicate that sulfate in solution may inhibit dolomitization primarily by retarding the rate of calcite dissolution, rather than by inhibiting the direct precipitation of dolomite from solution. The rate of calcite dolomitization was greater in solutions with higher carbonate/bicarbonate concentrations. This provides some confirmation for hypotheses regarding the importance of carbonate in solution as a kinetic factor that expedites dolomitization.