During the summer of 1976, 130 air-filter samples were collected at 10 sites in the Washington, D.C., area and analyzed for 39 elements, with 37 samples also being analyzed for SO/sub 4//sup 2 -/, NO/sub 3//sup -/, and NH/sub 4//sup +/. Concentration patterns were interpreted by using chemical element balances for seven sources: coal, oil and refuse combustion, soil dust, motor-vehicle emissions, limestone, and marine aerosols. For 35 nonvolatile elements, predicted concentrations were, on the average, within a factor of 1.93 of observed values. Predicted concentrations of primary particulate matter plus SO/sub 4//sup 2 -/, NO/sub 3//sup -/, and NH/sub 4//sup +/ account for 65% of measured total suspended particulate (TSP) matter, the remainder presumably being condensed water, organic material, and sources not included. The largest fraction of primary TSP matter is soil, dust, much of which is entrained by urban activities. The limestone component may originate from agricultural liming, construction projects, or abrasion of concrete. Most elements are reasonably well fitted, major exceptions being Cr, Cu, Ni, and a small-particle component of Mn.