Laboratory dissolution of Middle Ordovician rock samples from central Pennsylvania was studied at 23°C and 1 atm carbon dioxide pressure. Carbonate dissolution rates were compared at 22% bicarbonate saturation with respect to both calcite and dolomite. The results show that carbonate lithology exerts a strong influence on the dissolution rate and hence on the degree of cavity development in karst aquifers. The dissolution rate is most significantly affected by dolomite and impurity content. The rate decreases as percentages of dolomite and disseminated insolubles increase. Maximum dissolution rates occur for carbonate rocks with 1.0–2.5% MgO content and having abundant silty streaks. The sparite content is inversely related to cave development but is independent of dissolution rates measured under the laboratory conditions adopted in this study.