The MAP3S Precipitation Chemistry Network consists of four sites (to be expanded to 8 to 12) located in a north-south line from northern New York State to northwestern Virginia. Precipitation event samples are collected by cooperating site operators, using specially developed sampling equipment. The concentration data collected over the period September 22, 1976 (first collected sample) to July 1, 1977, are listed as a summary of the data reported monthly throughout the year. Samples were chemically analyzed at a central laboratory for 11 pollutant species, pH, conductivity, SO/sub 2/, SO/sup 2 -/, NH/sub 4//sup +/, NO/sub 2//sup -/, NO/sub 3//sup -/, Cl/sup -/, PO/sub 4//sup 3 -/, Na/sup +/, and K/sup +/, using ion chromatography, automated wet chemistry, atomic absorption spectrophotometry, and other standard techniques. The new precipitation collector equipment was evaluated by comparing the concentrations measured with those from a proven type of collector, operated simultaneously at all four sites.