The concentrations of major ions were determined in 155 representative, small, pristine lakes in southern Norway. The chemistry of these lakes appears to be governed by three factors: atmospheric inputs of seawater salts supply most of the Cl and Na; acid precipitation supplies most of the SO, and II I; and terrestrial inputs of chemical weathering products account for most of the Ca, Mg, and IIC03.The interaction of acid precipitation and geologic environment largely explains pH levels in these lakes. Lakes in granitic terrains have low concentrations of major ions, low buffer capacities, and are often acidic (pH < 5) when located in areas subject to acid precipitation. Sulfate is the major anion. Lakes in granitic terrains that do not receive highly acidic precipitation have pH levels >5.5, and bicarbonate is the major anion.