The study areas and methods are described for research on acidic streamflow episodes in five forest stream/catchment systems in the northern Appalachian Plateau region of Pennsylvania. Research was conducted from October 1988 to April 1990 and involved both hydrochemical and biological studies. Hydrochemical monitoring included measurements of stream discharge; in situ stream pH, conductivity, and temperature; air temperature, precipitation amounts and intensity, snowpack water equivalents, and snowpack melt rates. Intensive stream sampling during selected events using computer-controlled automatic samplers was used to document episodic stream chemistry. Stream samples were analyzed for a complete suite of common cations and anions along with acid neutralizing content, DOC, total monomeric aluminum, and organic monomeric aluminum. Biological impacts of acidic streamflow episodes on native brook trout and sculpin were assessed using electrofishing, in-situ bioassays, radiotelemetry, and spawning surveys. A rigorous quality assurance/quality control program was established for all measurements during the study, especially for water chemistry.