As part of a continuing study of diesel exhaust aerosol characteristics, the U.S. Bureau of Mines has applied chemical mass balance (cmb) model source apportionment analysis to evaluate a size- selective sampling method for determining the separate diesel exhaust and coal dust aerosol concentrations in a diesel-equipped coal mine. Size-selective sampling was used under the premise that diesel exhaust aerosol dominates the submicrometer aerosol size range, while most of the mineral dust aerosol is greater than 1 um. The cmb analysis, applied to both the fine and coarse fractions of the respirable mine aerosol, yielded the mass concentration contributed to each by diesel exhaust and mineral dust aerosol sources. The moudi size distribution data were analyzed using nonlinear regression to parameterize the fine and coarse fractions of the sampled aerosol and to estimate the contributions to each fraction from both coal dust and diesel aerosol sources. For the diesel mine visited, analysis of the moudi samples yielded a value for the fraction of the fine aerosol attributable to coal dust of 15 +/- 7 pct fine fraction coal from analysis of the moudi samples versus 25 +/- 4 pct from the cmb analysis. The remainder of the fine aerosol in the mine was diesel exhaust aerosol. After correcting for the presence of coal dust in the fine aerosol fraction, analysis of the moudi size distributions yielded estimates of respirable mineral and diesel exhaust aerosol concentrations that were accurate to within 10 pct of values determined by the cmb apportionment.