The Bureau of Mines, U.S. Department of the Interior, as part of the National Acid Precipitation Assessment Program, is conducting a field exposure program to measure the corrosion damage on commonly used structural metals and the incremental effects of acidic deposition and other environmental variables. Corrosion damage, air quality, rain chemistry and meteorology are being continuously measured at 5 sites in the Eastern and Midwest U.S. for periods up to 84 months. Corrosion damage on zinc for periods up to 36 months was determined from weight-loss measurements, analysis of corrosion film chemistry and precipitation runoff chemistry. The long-term zinc corrosion film may consist of a stable inner layer sensitive to atmospheric SO sub 2, and a non-protective outer layer. Dry deposition of SO sub 2 and NO sub 2 is significant. Zinc losses from the corrosion film are proportional to H sub L.