||Dry deposition is thought to be as important as wet deposition in acidifying ecosystems. However, at present acidic dry deposition of relevant particles and gases cannot be monitored directly in a quantitative manner. The U.S. EPA Workshop on Dry Deposition (Report No. EPA-600/9-80-050) recommended that dry deposition velocities be parameterized as a function of micrometeorology and surface type to permit the use of ambient pollutant concentration data for inferring dry flux ('concentration monitoring' technique). Also, the micrometeorological technique's variance, modified-Bowen ratio, and eddy accumulation were identified as candidates for development as dry flux monitors for network stations. This approach has been adopted by the task group on 'Deposition Monitoring of Acidic Substances' of the Interagency Task Force on Acid Precipitation. Research monitoring stations have been established at Oak Ridge, TN, Argonne, IL, and University Park, PA for the purpose of intercomparing 'concentration monitoring', the three previously identified micrometeorological techniques, and eddy correlation. Intercomparison tests are being performed for SO2, NO2, HNO3, NH3, O3, and particulate SO4(-2), NO3(-1), and NH4(+1). The status of methods development and performance is presented.