The pH-dependence of silicate mineral weathering rates was measured in small-plot experiments at the Bear Brooks Watershed Manipulation Project site in Maine, USA. Six 2 sq m plots were acidified with solutions of HCl in deionized water at pH values of 2, 2.5, and 3. Acid application was at the rate of 3 cm/week for approximately 26 weeks per year for 2 years. Soil solutions were collected by tension lysimeters at 25 and 50 cm depths. The composition of the soil solutions, together with the grain-size distribution and mineralogy of the soil, were used to calculate mineral weathering rates. In the lab experiments, the dependence or base cation release rates on pH varied from cation to cation, reflecting the different behavior of different minerals. Dissolution rates observed in the field, normalized on the basis of geometrical mineral surface area, were smaller than laboratory rates by a factor of about 200. Laboratory dissolution experiments can be used to predict the pH-dependence of mineral weathering in the field, but not absolute rates.