A source apportionment workshop sponsored by the United States Environmental Protection Agency was held at Quail Roost Conference Center in Rougemont, N.C. Thirty-five scientists from academic, governmental, and private institutions participated. The objective was to compare and document results of source apportionment analyses of simulated and real aerosol data sets. The simulated set was developed by scientists from the National Bureau of Standards and consisted of mass and elemental concentrations generated using a dispersion model that simulated transport of aerosols from a variety of sources to a receptor site. The real set contained the results of x-ray fluorescence, combustion, ion chromatography, x-ray diffraction, and scanning electron and optical microscopy analyses of aerosol samples collected in 18 12-hr sampling periods in Houston, TX. Ten groups analyzed these data sets using a variety of receptor models to apportion the simulated and real ambient measurements to potential contributing sources.