Using a set of data on aerosol composition in Houston, TX, nine participants of the Quail Roost II receptor modeling workshop estimated impacts of major classes of emission sources. The data set included mass, elemental composition, and ionic composition of fine- and coarse- fraction aerosol collected at the University of Houston during 18 12-hr periods from Sept 10 to 19, 1980. Methods used to analyze this data set included chemical mass balance, ridge regression, multiple linear regression, and target transformation factor analysis. Some participants performed additional analyses using x-ray diffraction, scanning electron microscopy, and light microscopy. The number of classes detected ranged from 4 (by multiple linear regression) to 23 (by light microscopy). The results were condensed into eight general categories, intercompared, and found to agree favorably. Differences in results were associated with the use of different source profiles.