Much of the emphasis in the National Acid Precipitation Assessment Program (NAPAP) has been on historical or longterm trends in surface water acidification. Short-term acidic episodes, however, also might have significant adverse effects on aquatic ecosystems. The U.S. EPA is presently designing an Episodic Response Project to investigate the regional extent, frequency, duration and magnitude of acidic episodes. The studies discussed in the report, however, were conducted under NAPAP Task Group E2-Aquatic Effects. A total of four episodic studies were conducted in the Catskill Mountains of New York (Murdoch, USGS), Laurel Hills, PA (Witt and Barker, USGS), Southern Blue Ridge Province, NC, TN (Olem, TVA), and Ouachita Mountains, AR (Nix et al., Ouachita Baptist University).