Acid precipitation has been measured in many areas of California, including the Sierra Nevada. This region is characterized by high-elevation, granite-based lakes which may be sensitive to acid inputs. Possible damage to these aquatic systems due to continued acid deposition was investigated during a program of field monitoring and laboratory microcosm experiments. During 1979-1981 Sierra lake water samples were analyzed for pH, alkalinity, and concentrations of major and minor cations. Microcosm systems, established in a controlled laboratory environment using lake and sediments, were treated with nitric acid and then analyzed for changes in chemical and biological variables.